Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19.

1
CESS Colson 2020
Dossier Cubrebocas y mascarillas protectoras
en la pandemia Covid-19.
Actualizado a 30 de abril, 2020
Centro de Estudios en Salud y Sociedad1
Contenido
Presentación: Uso razonado de protectores faciales en la pandemia Covid-19: un enfoque bio-socio-cultural. ............ 5
Mohan, A. y A. Misra. 1996. Use of facial masks during a plague epidemic. Letters to editor. British Medical Journal 72
(844): 127....................................................................................................................................................................... 11
Pallarito, Karen (6 de noviembre, 2009) “Respirator or face mask? Best H1N1 protection still debated”. Healthcom. 13
Johnson, D.F., J.D. Bruce, C. Birch y M. Grayson. 2009. A quantitative assessment of the efficacy of surgical and N95
masks to filter influenza virus in patients with acute influenza infection. Clinical Infectous Diseases 49 (2): 275-277. 15
Milton, D. et al. 2013. Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical
masks.PLoS Pathog. 9 (3): e1003205............................................................................................................................. 16
NIOSH-CDC. 2013. Conozca su respirador: Su salud podría depender de ello. .............................................................. 16
Milton, D., M. Fabian, B. Cowling, M. Grantham y J. McDevitt. 2013. Influenza virus aerosols in human exhaled breath:
particle size, culturability, and effect of surgical masks. PLoS Pathog 9 (3): e1003205. ................................................ 22
1
Elaborado por Jesús Armando Haro. Correo electrónico: aharo@colson.edu.mx

2
Dossier Cubrebocas y mascarillas protectoras en Covid-19
Mniszewski, Susan, Sara Del Valle, Reid Priedhorsky, James Hyman y Kyle Hickman. 2013. Understanding the impact of
face mask usage through epidemic simulation of large social networks. En Theories and Simulations of Complex Social
Systems, pp 97-115. ....................................................................................................................................................... 23
Smith, Sheree M. et al. 2015. Use of non-pharmaceutical interventions to reduce the transmission of influenza in adults:
A systematic review. Respirology. 20 (6): 896–903........................................................................................................ 41
Barasheed, O, M. Alfelali, S. Mushta et al. 2016. Uptake and effectiveness of facemask against respiratory infections at
mass gatherings: a systematic review. Int J Infect Dis.................................................................................................... 42
Sander, Herfst, Michael Böhringer, Basel Karo, Philip Lawrence, Nicola S. Lewis et al. 2017. Drivers of airborne human-
to-human pathogen transmission. Current Opinion in Virology 22 (February): 22-29................................................... 44
Uchida, M. et al. (6 de diciembre, 2016). Effectiveness of vaccination and wearing masks on seasonal influenza in
Matsumoto City, Japan, in the 2014/2015 season: An observational study among all elementary schoolchildren Prev
Med Rep. 2017 5: 86–91. ............................................................................................................................................... 54
Offedu, V. et al. 2017. Effectiveness of masks and respirators against respiratory infections in health care workers. Clin
Infect Dis 65 (11): 1934-1942. ........................................................................................................................................ 55
CDC 2019. FAQ about protective equipment: Respirators............................................................................................. 56
CDC. 2019. Recomendación sobre el uso de cubiertas de tela para la cara, especialmente en las áreas con transmisión
comunitaria significativa. ............................................................................................................................................... 59
Gajanan, Mahita (31 de enero, 2020) “Can face masks prevent coronavirus? experts say that depends” Time......... 61
Lynteris, Christos (17 de febrero, 2020) “¿Cuál es la verdadera razón por la que la gente usa mascarillas durante una
epidemia?” The New York Times.................................................................................................................................... 63
Secon, Holly (26 de febrero, 2020). “People are racing to buy face masks amid the coronavirus outbreak, but they
probably won't protect you from illness” Bussiness Insider........................................................................................... 66
Cherney, Kristeen y Daniel Potter (18 de marzo, 2020) Does wearing a mask protect you from the flu and other viruses?
....................................................................................................................................................................................... 69
Froelich, Paula. (28 de marzo, 2020). “Experts say face masks can help slow COVID-19, despite previous claims” New
York Post. ....................................................................................................................................................................... 72
Feng, Shuo, Chen Shen, Nan Xia, Wei Song, Mengzhen Fan Benjamin J Cowling. 2020. Rational use of face masks in the
COVID-19 pandemic. The Lancet 20-03-2020................................................................................................................. 73
UN News (3 de marzo, 2020) “We can’t stop COVID-19 without protecting health workers’: WHO chief”. ................. 76
Oaklander, Mandy (4 de marzo, 2020) “Health experts are telling healthy people not to wear face masks for coronavirus.
So why are so many doing it? Time................................................................................................................................ 78
Li, R., S. Pei, B. Chen et al. (16 de marzo, 2020) Substantial undocumented infection facilitates the rapid dissemination
of novel coronavirus (SARS-CoV2) Science. eabb3221 DOI: 10.1126/science.abb3221................................................. 80
Gobierno de Canada (20 de marzo, 2020). Considerations in the use of homemade masks to protect against COVID-19.
Notice to General Public and Healthcare Professionals. ................................................................................................ 81
Ortiz, Marina (22 de marzo, 2020). “Coronavirus: cómo hacer tu propia mascarilla casera contra el Covid-19”. El Español
(Madrid). ........................................................................................................................................................................ 83
Letzter, Rafi. (24 de marzo, 2020) “Can homemade masks protect you from COVID-19?” LiveScience. ....................... 85
Huang, Sui (26 de marzo, 2020) “COVID-19: why we should all wear masks — there is new scientific rationale”. Medium.
....................................................................................................................................................................................... 87
Coren, Michael J. (27 de marzo, 2020) “Every expert opinion you’ve heard about wearing masks is right”. Quartz. ... 95
Sanders, Laura (27 de marzo, 2020) “Face mask shortages have sparked creative solutions. Will they work?” Science
News............................................................................................................................................................................... 99
Infobae. (29 de marzo de 2020). “Solidaridad y coronavirus: hacen barbijos y máscaras faciales 3D para cuidar la salud
de médicos y enfermeros”. .......................................................................................................................................... 101

3
CESS Colson 2020
Fabr, Ferris (30 de marzo, 2020) “It's time to face facts, America: masks work” Wired. ............................................. 105
Haridy, Rich (30 de marzo, 2020) “Should you wear a face mask? Experts divided over COVID-19 guidelines”. New Atlas.
..................................................................................................................................................................................... 110
RPP Noticias (Perú) (30 de marzo, 2020) “Coronavirus: Así deben ser las mascarillas que pueden ser confeccionadas en
casa y por las PYMES” .................................................................................................................................................. 113
InfoBae (1 de abril, 2020) “Francia y EEUU luchan por comprar mascarillas chinas". ................................................. 115
Leydon, Stephanie (1 de abril, 2020) “How much do homemade face masks really protect against COVID-19?” WGBH
(Boston)........................................................................................................................................................................ 116
Melillo, Gianna (1 de abril, 2020) “COVID-19 may be transmitted through the eye, report finds” AJCM-Newsroom. 118
W RADIO (Ciudad de México) (1 de abril, 2020) Gran error no usar mascarilla: principal científico en China ante COVID-
19. ................................................................................................................................................................................ 120
Hatmaker, Tayor (2 de abril, 2020) “CDC recommends Americans wear cloth masks to limit spread of COVID-19” The
Crunch. ......................................................................................................................................................................... 121
Facher, Lev (2 de abril, 2020) “White House expected to recommend Americans wear cloth masks to prevent
coronavirus spread” Stat News.................................................................................................................................... 123
Verificado (02 de abril, 2020) “Uso incorrecto de mascarillas genera falsa seguridad y aumenta riesgo de COVID-19”.
Salud con Lupa (Perú)................................................................................................................................................... 125
Secretaría de Educación Pública-Gobierno de México (2 de abril, 2020) “Desarrolla TecNM mascarilla con tecnología 3D
para médicos tratantes del COVID-19” Boletín SEP No 87........................................................................................... 128
Infobae (3 de abril, 2020) “¡Dejen de comprar mascarillas!” o “mascarillas para todos”: cómo cambió el criterio en
EEUU”........................................................................................................................................................................... 130
Leung, Nancy, Daniel Chu, Eunice Shiu et al. 2020. Respiratory virus shedding in exhaled breath and efficacy of face
masks. Nature Medicine. https://doi.org/10.1038/s41591-020-0843-2...................................................................... 136
University of Maryland. (3 de abril, 2020). “Wearing surgical masks in public could help slow COVID-19 pandemic's
advance: Masks may limit the spread diseases including influenza, rhinoviruses and coronaviruses." Science Daily. 139
Animal Político (3 de abril, 2020) “UNAM recomienda el uso de cubrebocas en lugares concurridos para evitar contagios
de COVID-19”. .............................................................................................................................................................. 141
The Guardian México. (3 de abril, 2020) “Coronavirus desata pelea mundial por conseguir mascarillas y cubrebocas”
UnoTV........................................................................................................................................................................... 143
HarCo (4 de abril, 2020). Recomendaciones y cotizaciones en protectores faciales. .................................................. 144
Brainard, J., N. Jones, I. Lakem L, Hooper y P. Hunter. (6 de abril, 2020). Facemasks and similar barriers to prevent
respiratory illness such as COVID-19: A rapid systematic review. medRxiv. ................................................................ 148
InfoBae (6 de abril, 2020) “Coronavirus en México: en qué estados ya es obligatorio el uso de cubrebocas”............ 155
Parker-Pope, Tara (10 de abril de 2020). “Así NO se usa el tapabocas” The New York Times. .................................... 157
El Blog del Buho (14 de abril, 2020) “Mascarillas, polímeros y tejidos no tejidos”. ..................................................... 159
Gorman, James (18 de abril, 2020) “Are face masks the new condoms? The New York Times. .................................. 162
Thomas, Jason (22 de abril, 2020) “Workarounds for the face masks shortage during COVID-19”. The Purple Quill.. 164
La Jornada Maya (24 de abril, 2020) “Datos importantes sobre el uso de cubrebocas” ............................................. 166
Cultura Colectiva (26 de abril, 2020) “A partir del lunes 27 de abril, será obligatorio el uso de cubrebocas en el espacio
público en la capital”.................................................................................................................................................... 169
Stern, Dalia, Nancy López. Carolina Pérez, Romina González, Francisco Canto y Tonatiuh Barrientos. 2020. Revisión
rápida del uso de cubrebocas quirúrgicos en ámbito comunitario e infecciones respiratorias agudas. Salud Pública de
México. https://doi.org/10.21149/11379.................................................................................................................... 170

4
Xiao, J., E. Shiu, H. Gao, J. Wong, M. Fong, S. Ryu y B. Cowling. 2020. Nonpharmaceutical measures for pandemic
influenza in nonhealthcare settings—personal protective and environmental measures. Emerging Infectious
Diseases 26 (5): 967-975. ............................................................................................................................................. 177
Wikipedia, the free enciclopedia N95 mask................................................................................................................. 191

5
CESS Colson 2020
Presentación: Uso razonado de protectores faciales en la
pandemia Covid-19: un enfoque bio-socio-cultural.
Jesús Armando Haro2
El debate actual sobre el uso de protectores faciales en la pandemia Covid-19
contiene varias aristas, que denotan que el asunto, lejos de acotarse a lo biológico y
epidemiológico en materia de prevención del contagio, incide en esferas
económicas, sociales, políticas y culturales. El rango de su prescripción va desde el
uso obligatorio implementado tempranamente por China, Corea, Japón y otros
países asiáticos, seguido luego por otros países, regiones o ciudades; con
recomendaciones variables para uso en público, permanente o selectivo, manejadas
de manera generalmente ambigua o cambiante, como sucedió en Estados Unidos,
al igual que con la Organización Mundial de la Salud, que desaconsejaron
inicialmente su uso, para recomendarlo después. En México, se ha intentado politizar
el asunto, culpando a las autoridades sanitarias de no hacerlos obligatorios, mientras
el Gobierno de la Ciudad de México, así como otras ciudades mexicanas, e incluso
estados, como Coahuila y Yucatán, han implementado su uso compulsivo en la vía
pública, a la par de otras medidas encaminadas a prevenir la transmisión del virus,
como restricción a la circulación de las personas, limitar los ocupantes por vehículo,
suspender actividades productivas no esenciales y difundir información sobre las
ventajas de quedarse en casa; lavarse las manos con frecuencia, guardar la sana
distancia, aislarse y dar aviso en caso de presentar síntomas.
Comprender lo que se debate en el caso de las mascarillas, nos lleva a advertir, en
primer término, dos aspectos que aunque son complementarios no dejan de ser
diferentes: la prevención pensada en términos individuales, yo y mi familia, y desde
la salud pública, lo que conlleva considerar que aquí lo relevante no es abolir sino
retrasar el contagio, “aplanar la curva para no sobrecargar los servicios de salud”. En
cambio, desde la prevención clínica, conviene distinguir las condiciones en las que
se encuentra cada grupo doméstico, donde cabría diseñar rutinas para familias con
miembros vulnerables por el riesgo de letalidad. El uso de protectores faciales debe
orientarse por una lógica que razone su uso para disminuir el riesgo de contagio, sin
olvidar que es solamente una medida complementaria que no impide absolutamente
la transmisión viral. Entenderlo, nos lleva a analizar la biología del SARS-2, el agente
causal de la Covid-19 y su recepción por el cuerpo humano.
2
Centro de Estudios en Salud y Sociedad, El Colegio de Sonora.

6
Este tipo de betacoronavirus mide entre .05 y 0.2 um (micrones) de diámetro. Es una
forma “vital” que solo puede expresarse sí infecta a células vivas, donde se reproduce.
Se transmite a través de gotículas y microgotículas que se esparcen respectivamente
en spray (partículas mayores de 10 um) y aerosol (menores de 10 um), con
secreciones orales y respiratorias, al hablar, estornudar o toser, siendo su período
promedio de incubación de 5.1 días, aunque la gran mayoría de casos cursan
asintomáticos, sin conocerse aun con precisión el tiempo en que se transmite. Las
partículas virales pueden evaporarse o caer al suelo dentro de dos metros, pero
también sobrevivir hasta 7 horas en ambientes cerrados, donde se esparcen a mayor
distancia, aunque disminuyendo su concentración, como sucede en superficies
plásticas y metálicas, donde persiste entre 3 horas y 9 días sí hay condiciones de
humedad, pues al parecer se inactiva relativamente pronto (una hora) bajo el sol, en
condiciones aireadas. Por ello, los protectores faciales no bastan, pues se señala
además que existe la posibilidad de que pueda adquirirse a través de las conjuntivas,
aunque es mucho más factible que la principal vía de ingreso sea la nasofaríngea,
donde hay abundantes proteínas ACE2 a las que se liga el virus. Aunque aun
desconocemos factores clave en su transmisión y marca inmune, los datos indirectos
acerca de otros coronavirus (SARS) sugieren que la infección por SARS–CoV–2
genera inmunidad tras la recuperación, aunque puede ser letal para quienes
necesitan ser hospitalizados, en su mayoría, tercera edad y enfermos crónicos,
aunque también han muerto jóvenes, adultos mas o menos sanos, embarazadas y
niños, incluso personal de salud.
En lo relativo a los protectores faciales, es muy distinta la capacidad de un
cubrebocas a la de un “respirador” N95, capaz de filtrar, como su nombre, sugiere,
hasta el 95% de las partículas aéreas, gracias a su filtro de nanofibras de
polipropileno, garantizado para no dejar pasar microgotículas, aunque no sirve para
gases o vapores, a pesar de crear un sello hermético de boca y nariz que incomoda
en uso prolongado, y aunque son más caras, se consideran reusables. En cambio, los
cubrebocas o mascarillas quirúrgicas, solo proveen protección contra gotículas
visibles; son útiles para obstaculizar partículas grandes que pueden contener virus,
bacterias u otros gérmenes, pero no a los del aerosol de las microgotículas. Se
consideran desechables. A contrapelo, las mascarillas artesanales, aun cuando no son
muy efectivas -pues se hacen de diversos materiales-, constituyen una barrera
especialmente útil para no transmitir a los demás, siendo en su mayoría reusables
previa desinfección. Hay que tomar en cuenta que desde la influenza “española” de
1918 se comenzó a usar protectores faciales como medida preventiva. En 1972, la
empresa 3M desarrolló el primer respirador capaz de filtrar micropartículas, con
tecnología desarrollada para fabricar brassiers. Desde antes de la pandemia de gripe

7
CESS Colson 2020
A (H1N1) de 2009, se comenzó a debatir sobre la utilidad preventiva tanto de
cubrebocas como respiradores N95, especialmente en trabajadores de la salud,
siendo en 2013 cuando el National Institute for Occupational Safety and Health
(NIOSH) en Estados Unidos, implementó su uso obligado en hospitales con riesgo
de contagios respiratorios. Diversos estudios efectuados evidencian hallazgos
propicios para recomendar el uso de ambos en circunstancias específicas. Como
varios investigadores señalan, en todo caso, siempre es mejor portar alguna barrera
sí se considera no solamente la posibilidad del contagio, sino también la intensidad
o carga viral de la exposición (Milton et al 2013).
Nuestro sistema inmunológico tiene posibilidades de salir mejor librado con una
carga mínima, incluso repetida, que a una invasión masiva de virus. Otros trabajos
señalan los efectos negativos del uso prolongado del mismo cubreboca o mascarilla,
aduciendo que el aliento las humedece y eso favorece la creación de reservorios para
diversos microorganismos, por lo que se recomienda usarlas por tiempo limitado o
cambiarlas, además de cuidar otras medidas, como no tocarla por el frente al
quitársela, proceder a desinfectarla, con varios métodos. Se han publicado además
investigaciones que resaltan los impactos culturales de los protectores, su
incremento de acuerdo a la incidencia de casos y cómo inciden en el distanciamiento
físico, destacando que rara vez fueron usados de manera única, sino en conjunto con
otras medidas preventivas, como el lavado de manos, el cierre, control y sanitización
de superficies en espacios públicos, el estornudo de cortesía. Algunos trabajos
concluyen que los protectores faciales son quizás la medida preventiva de mayor
costo-beneficio, estimando una reducción de contagios de 10% en la población
general y hasta del 50% en quienes las portaron (Mniszewski et al 2013).
Durante la pandemia actual, el uso de los protectores faciales se ha politizado, a
partir especialmente de la especulación subsecuente a la alta demanda y la escasez
mundial, que ha incrementado, por ejemplo, el precio de la N95 de 0.65 centavos de
dólar a casi tres por unidad, además de provocar actos internacionales parecidos a
la piratería. La escasez contrasta con la contaminación registrada en varias playas del
mundo con los desechos y con los justos reclamos del personal de salud a nivel
nacional e internacional; también con la creatividad para diseñar diversos tipos de
protectores, incluyendo los de máscara total en 3D, los artesanales estampados o
bordados, incluso de palma; o respiradores de sello hermético fabricados con toallas
industriales, mallas de cobre y otros “tejidos no tejidos” de polímeros. Varias
revisiones sistemáticas (Stern et al 2020, Xiao et al 2020) señalan que los estudios no
son concluyentes, pero, en su metodología, basada en meta-análisis y revisiones
sistemáticas, excluyen la mayoría de miles de trabajos realizados, debido a que no

8
cumplen con ciertos criterios estipulados, como la selección de las muestras, la
ausencia de pruebas adecuadas y otras estrategias de control, para culminar
diciendo que la información no es concluyente por no ser consistente ni comparable,
desechando con ello hallazgos relevantes, como experimentos comunitarios en
escuelas japonesas, donde los cubrebocas demostraron ser tan efectivos como las
vacunas (Uchida et al 2017), o ensayos clínicos controlados en servicios de salud,
cuya revisión sistemática denotó la eficacia de cubrebocas y respiradores para
prevenir infecciones respiratorias agudas (Offedu et al 2017), mientras que otras
revisiones resaltan la sinergia de los protectores cuando se combinan con el lavado
de manos (Smith 2015).
Tampoco mencionan porqué especialistas que tienen años investigando sobre el
tema, como Nancy Leung, Shan Soe-Lin, Robert Hecht, George Gao y Raina
MacIntyre, entre otros, recomiendan el uso de cualquier tipo de protección como
medida tanto personal como colectiva, pues, finalmente se trata de reducir el ritmo
de incidencia y no de abolir el contagio, para lo cual sería quizás necesario masificar
el uso de las N95 a nivel comunitario, así como aplicar otras medidas ya
comprobadas, incluyendo además de las descritas, el monitoreo de temperatura, el
seguimiento de casos y contactos, los test a sospechosos y muestreos centinela, que
debieran sumarse a una estricta restricción domiciliaria. Pero no sería deseable para
la inmunidad de grupo, como tampoco lo es prolongar demasiado tiempo la
cuarentena, por sus impactos económicos y sociales. Aunque todavía se desconocen
los efectos climáticos en la biología del virus, resta por comprobar la efectividad de
otras prácticas, como la ventilación de espacios públicos (Gao et al 2016), la
humidificación de ambientes secos (Reiman et al 2018) y el uso selectivo de luz
ultravioleta para desinfectar objetos (McDevitt et al 2012). Por esto, el uso razonado
de protectores se justifica tanto clínicamente en casos vulnerables como a nivel
colectivo, pues hay trabajos recientes que sugieren que casi 80% de los contagios
ocurre mediante contacto con personas que no son diagnósticadas, como se
demostró en China (Li et al 2020). También, trabajos (Backer 2020) que sugieren la
influencia de la luz solar, en la transmisión y curso de Covid-19, siendo el ejercicio
una de las pocas estrategias comprobadas para aumentar la inmunidad.
Christos Lynteris, escribió recientemente en The New York Times, “Comprender las
epidemias no solo como sucesos biológicos, sino también como procesos sociales
es clave para una contención exitosa. Los miembros de una comunidad usan
mascarillas no solo para protegerse de la enfermedad. También las usan para
demostrar que quieren estar, y sobrellevar, juntos el flagelo del contagio”. Esto nos
señala uno de los cambios culturales de la pandemia presente, donde está dejando

9
CESS Colson 2020
de ser causa de estigmatización para convertirse en marca de cortesía. Si bien se
alude que usar mascarilla puede llevar a soslayar el resto de las medidas, como
desinfectar los artículos que se traen a casa o quitarse los zapatos, en la práctica uno
observa que al llevarla se facilita mantener la atención en estas y otras preventivas,
actuando como recordatorio. No obstante, su uso razonado depende de la persona
y el contexto. Sí a nivel doméstico se cuida a una persona vulnerable se recomienda
la mascarilla quirúrgica o cubrebocas, solo en los momentos cercanos. Sí se trata de
salir, portarla únicamente en lugares donde no se garantiza la sana distancia o se
encuentran cerrados, sin ventilación natural, para lo cual lo mejor es conseguir una
mascarilla artesanal, preferentemente fabricada con nanofibras sintéticas. Sí se
tienen síntomas, no salir más que para ir al médico, en cuyo caso, es muy importante
portar protección todo el tiempo. Su uso en personas que no están en restricción
domiciliaria, como los comerciantes y otros trabajadores, debe guiarse por las
circunstancias en aglomeración, como el transporte público.
Las N95 hay que dejarlas para el personal de salud, pues están escasas y ya son casi
dos mil trabajadores de la salud que han sido infectados en México. Sí acaso ya
contamos con una, recordar que no se recomienda usar más de 5 veces, aunque con
el principio relativo y complementario que se recomienda, puede alargarse su uso sí
se desinfecta con agua y jabón y se seca al sol. Actualmente tiende a consolidarse la
evidencia del importante papel que tienen los portadores asintomáticos del virus en
la transmisión de la enfermedad, por lo que el protector se perfila como una medida
sensata para incorporarse colectivamente, lo cual requiere diseñar modelos y modos
de uso acordes a lo que cada situación amerita en lo particular, con criterios
bioecológicos, socioeconómicos y culturales. El asunto denota que el sentido común
necesita de la ciencia, pero que está también debe beneficiarse del buen sentido,
referido a lograr más con pocos recursos.
Referencias
Bäcker, Alex (13 de abril, 2020) “Follow the sun: slower COVID-19 morbidity and
mortality growth at higher irradiances”. SSRN.
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3567587.
Gao, X., J. Wei, B. Cowling e Y. Li. 2016. Potential impact of a ventilation intervention
for influenza in the context of a dense indoor contact network in Hong Kong. Sci
Total Environ 569-570: 373–381.
Li, R., S. Pei, B. Chen B, et al. 2020. Substantial undocumented infection facilitates the
rapid dissemination of novel coronavirus (SARS-CoV2). Science.

10
Lynteris, Christos (17 de febrero, 2020) “¿Cuál es la verdadera razón por la que la
gente usa mascarillas durante una epidemia?” The New York Times
McDevitt, J., S. Rudnick y L. Radonovich. 2012. Aerosol susceptibility of influenza
virus to UV-C light. Appl Environ Microbiol: 78: 1666–1669.
Milton, D. et al. 2013. Influenza virus aerosols in human exhaled breath: particle size,
culturability, and effect of surgical masks. PLoS Pathog. 9 (3): e1003205.
Mniszewski, Susan, Sara Del Valle, Reid Priedhorsky, James Hyman y Kyle Hickman.
2013. Understanding the impact of face mask usage through epidemic simulation of
large social networks. En Theories and simulations of complex social systems, pp 97-
115.
Offedu, V. et al. 2017. Effectiveness of masks and respirators against respiratory
infections in health care workers. Clin Infect Dis 65 (11): 1934-1942.
Smith, Sheree M. et al. 2015. Use of non-pharmaceutical interventions to reduce the
transmission of influenza in adults: A systematic review. Respirology. 20 (6): 896–903.
48.
Reiman, J.M. et al. 2018. Humidity as a non-pharmaceutical intervention for influenza
A. PLoS One 3:e0204337.
Shephard, R., T. Verde, S. Thomas y P. Shek. 1991. Physical activity and the immune
system. Canadian Journal of Sport Sciences 16 (3): 169–185.
Stern, Dalia, Nancy López, Carolina Pérez, Romina González, Francisco Canto y
Tonatiuh Barrientos. 2020. Revisión rápida del uso de cubrebocas quirúrgicos en
ámbito comunitario e infecciones respiratorias agudas. Salud Pública de México.
https://doi.org/10.21149/11379.
Uchida, M. et al. 2017. Effectiveness of vaccination and wearing masks on seasonal
influenza in Matsumoto City, Japan, in the 2014/2015 season: An observational study
among all elementary schoolchildren. Prev Med Rep. 5: 86–91.
Xiao, J., E. Shiu, H. Gao, J. Wong, M. Fong, S. Ryu y B. Cowling. 2020.
Nonpharmaceutical measures for pandemic influenza in nonhealthcare settings—
personal protective and environmental measures. Emerging Infectious Diseases 26
(5): 967-975.

11
CESS Colson 2020
Mohan, A. y A. Misra. 1996. Use of facial masks during a
plague epidemic. Letters to editor. British Medical Journal
72 (844): 127.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2398361/pdf/postmedj00014-0065a.pdf
Sir, During the recent outbreak of pneumonic plague in India, we witnessed the unusual spectacle
of numerous 'masked men' (and women) moving about in the streets and public places of Delhi -
apparently to protect themselves from the plague. This was particularly evident in the hospitals,
where medical and paramedical personnel, especially those manning the emergency services, were
observed to be moving around with masks hanging round their necks, and in their pockets, which
were taken out and used when a patient was examined. Interestingly, a variety of face-masks were
used by the general public, including masks made from paper, gauze of various
weaves, plastic, synthetic material and cloth. Towels, sarees, lehangas and
chunnis (scarf-like pieces of cloth) were also draped over the face to serve as
impromptu masks. Enterprising businessmen exploited this mass (mask) hysteria by piecing
together pieces ofpaper or fabric with cloth or elastic strips and selling them as face-masks, at an
exorbitant price of Rupees 5 to 10 each. We were curious about certain aspects of these face-masks:
(a) whether there were any studies which objectively assessed the efficacy of face-masks in the
prevention of infections in general, and pneumonic plague in particular, (b) which type of face-mask
is optimally protective, and (c) how often should a facemask be changed to prevent acquisition of
infection. We found an interesting divergence of opinion.' We were
surprised to learn that there were no objective studies available on the efficacy of
face-masks in the prevention of pneumonic plague. Manson's textbook2 states that
'a mask of absorbent cotton wool (16 x 12 cm) enclosed in muslin, and retained in position by a
many-tailed gauze bandage, together with goggles, rubber gloves and cotton uniform proved
thoroughly effective'. No further details were forthcoming from the literature. Most of the studies
of face-masks referred to their efficacy in preventing wound infection in the operating theatre, and
among dental surgeons.35 Salient features from the literature are summarised below. * Most
of the particles or organisms that penetrated the supposedly
efficient filter masks were < 5 gim in diameter and could
reach the alveoli of the lungs. Thus, facemasks cannot replace effective

12
chemoprophylaxis as a viable preventive option. * Aerosols can remain suspended in air for about
half an hour. Hence, crowded outpatient clinics or casualty are never free from airborne
contamination. To be fully effective, face-masks should therefore be worn continuously over nose
and mouth. * In an environment replete with infectious aerosol, the risk
of cross-contamination between the physician and his patient(s) is
increased if one mask is worn for a prolonged period. In such a
situation, the outer surface of the mask becomes a nidus for
pathogenic organisms. The ideal time interval for changing masks is
not known, however. At the time of the most infectious phase of the recent outbreak of
pneumonic plague none of the above-mentioned guidelines were observed, even by the most
knowledgeable physicians. On the basis ofthe above observations and experience, the following
guidelines are recommended in epidemics of a highly infectious nature such as pneumonic plague:
(a) proper face masks should be worn, continuously covering nostrils and mouth, (b) to decrease
the entry of particles

13
CESS Colson 2020
Pallarito, Karen (6 de noviembre, 2009) “Respirator or face
mask? Best H1N1 protection still debated”. Healthcom.
November 6, 2009 -- Updated 2216 GMT (0616 HKT)
(Health.com) -- A preliminary report suggesting that N95 respirators -- filtering devices worn
over the mouth and nose -- protect against swine flu better than surgical face masks seems to
be incorrect, researchers revealed during a meeting of the Infectious Diseases Society of
America (IDSA).In fact, surgical face masks, which are cheaper and easier to wear, may be
just as good as N95 respirators. At the very least, researchers can't prove that one is better
than the other. It's the latest wrinkle in a continuing debate over how to protect health-care
workers from the H1N1 virus, also known as swine flu.
Raina MacIntyre, Ph.D., a professor of infectious diseases epidemiology and the head of the
University of New South Wales School of Public Health and Community Medicine, in Sydney,
Australia, says the research team didn't exactly retract the findings."We simply did the analysis
of the same data differently for the final paper," she explains. For the new analysis, the
researchers removed a control group of nearly 500 health-care workers and made other
statistical adjustments. Ultimately, the difference in infection rates between mask and respirator
users was not statistically significant. "[The study] still shows a likely superiority of N95s, with
half the rate of infection compared to surgical [masks]," MacIntyre says. "But the study was
probably underpowered to pick up statistical significance when we removed the control group."
"I would certainly wear an N95 respirator if I were exposed to infectious
patients," she adds. The N95 respirator is a tightly fitted facial mask designed to filter out
even very fine airborne particles, according to the U.S. Food and Drug Administration. Looser-
fitting surgical masks protect against large-particle droplets, splashes, sprays, or splatter, the
FDA says, but they don't completely block the germs from coughs and sneezes.
To figure out which protective device is best, MacIntyre and her colleagues tracked hospital
workers in Beijing, China, who wore surgical masks or N95 respirators, and compared rates of
influenza and respiratory illness. Preliminary findings were presented at a meeting of the
Interscience Conference on Antimicrobial Agents and Chemotherapy in September 2009. Final
results have yet to be published. The only other randomized clinical trial comparing health-care
workers' use of respirators and surgical masks was published online in October 2009 in the
Journal of the American Medical Association. Canadian researchers reported no difference in
influenza rates among nurses using one type of protective device versus the other. Both studies
helped inform an Institute of Medicine (IOM) panel that, in September 2009, issued a report
recommending the use of fitted N95 respirators by health-care workers who interact with patients
with confirmed or suspected cases of H1N1. (MacIntyre was also a member of that panel.)
However, because the two studies were preliminary, the committee said that it could not draw
conclusions from either."The take-home message for me is that, in clinical settings, wearing a
mask or an N95 appears to be essentially equivalent," says Mark E. Rupp, M.D., a professor of
infectious diseases at the University of Nebraska Medical Center in Omaha and president of the

14
Society for Healthcare Epidemiology of America (SHEA). Data presented at the IDSA meeting
also highlighted the problems with N95 respirators, Rupp says. Health-care workers say that the
respirators are uncomfortable and more difficult to wear than face masks, and that they make it
hard to speak with patients, among other problems, he explains. They're more expensive
too.Although respirator use made sense at the beginning of the swine flu pandemic, it now
appears that H1N1 behaves similarly to seasonal influenza, Rupp says, so "it doesn't make much
sense to be using different precautions for seasonal flu than we use for H1N1."The SHEA would
like to see federal guidelines revised, he says. Still, government health and safety organizations
are standing by the more stringent standard of protection.IOM spokeswoman Christine Stencel
says that the National Institute for Occupational Safety and Health and others have provided
"convincing data" on the ability of the respirators to filter out a large percentage of tiny
particles."Based on all the available evidence and data that the committee had to look at, [it
recommended] that the N95 respirator afforded the best potential protection against airborne
transmission of the virus, and therefore that was the recommendation for health-care workers in
terms of respiratory protection," she says. The Centers for Disease Control and
Prevention developed its policy independently of the IOM and the MacIntyre study, explains CDC
spokesman Jeff Dimond. However, it's similar in terms of respirator use. The CDC recommends
that health-care workers in close contact with people with suspected or confirmed H1N1
influenza use a properly fitted, disposable N95 respirator, or something that offers similar or
better protection.The current recommendation is based on unique conditions associated with the
existing pandemic, including low levels of population immunity to 2009 H1N1, the potential for
health-care personnel to be exposed to H1N1 patients, and other factors, Dimond says. In
October 2009, the Occupational Safety and Health Administration (OSHA) said it would soon
issue a "compliance directive" to ensure that health-care facilities have controls in place to
protect workers from occupational exposures to swine flu. OSHA said its directive would closely
follow the CDC's guidance.
In Rupp's opinion, the respiratory protection debate has distracted from other crucial flu-fighting
measures. These include:
• Quickly identifying and isolating patients with influenza-like illness.
• Preaching respiratory etiquette programs. Patients who are ill should be asked to wear a
surgical mask to contain their secretions, he says, and they should use tissues and wash their
hands frequently to prevent touch contamination.
• Encouraging hospital visitors to stay home if they're sick and urging health-care workers to stay
home when they're sick.
• Getting seasonal and H1N1 vaccines. "For health-care workers, that is by far the best way to
protect them," he says.

15
CESS Colson 2020
Johnson, D.F., J.D. Bruce, C. Birch y M. Grayson. 2009. A
quantitative assessment of the efficacy of surgical and N95
masks to filter influenza virus in patients with acute
influenza infection. Clinical Infectous Diseases 49 (2): 275-
277.

16
Milton, D. et al. 2013. Influenza virus aerosols in human
exhaled breath: particle size, culturability, and effect of
surgical masks.PLoS Pathog. 9 (3): e1003205.
Published online 2013 Mar 7. doi: 10.1371/journal.ppat.1003205 PMCID: PMC3591312 Donald K.
Milton, 1 , 2 , * M. Patricia Fabian,# 2 , 3 Benjamin J. Cowling, 4 Michael L. Grantham, 1 and James
J. McDevitt# 2
Abstract Author Summary NIOSH-CDC. 2013. Conozca su
respirador: Su salud podría depender de ello.
DHHS (NIOSH) publicación N.º 2013-138
junio de 2013
Instituto Nacional para la Seguridad y Salud Ocupacional (NIOSH)
Equipo de protección personal (EPP) para trabajadores de la salud
La verdad sobre los respiradores

17
CESS Colson 2020
Tenga la certeza de que está aprobado por NIOSH.Uno de los peligros ocupacionales en el entorno
de la salud es la transmisión aérea de ciertas enfermedades infecciosas.1
El potencial de exposición
no se limita a los médicos, enfermeros y personal de apoyo que atiende directamente a pacientes.
Abarca también a las personas que entregan comidas, limpian las habitaciones de los pacientes y
hacen trabajos de mantenimiento. Todas las personas que trabajan en áreas donde hay pacientes
infectados con enfermedades de transmisión por el aire están en posible riesgo.Una línea de
defensa vital es el uso de protección respiratoria adecuada cuando sea necesario. El respirador N95
con mascarilla de filtrado es el que más se usa en el ámbito de la salud.Tanto empleadores como
empleados deben seguir las normas de salud y seguridad establecidas por la Administración de
Seguridad y Salud Ocupacional (OSHA, por sus siglas en inglés), la Comisión Conjunta, la
Administración de Alimentos y Medicamentos (FDA, por sus siglas en inglés), los Centros de Servicios
de Medicare y Medicaid, y otras organizaciones.
Es importante que tenga en cuenta las siguientes consideraciones con respecto a los productos de
protección respiratoria:
Siga las pautas del programa de protección respiratoria de su organización; esto incluye tener la
aprobación médica necesaria
Asegúrese de estar usando un respirador aprobado por NIOSH.
Haga que le hagan una prueba de ajuste del respirador anualmente.
Sepa cómo ponerse y sacarse el modelo y la marca de respirador específico que use.
Sepa cómo usar el respirador de manera segura y eficaz.
Dispositivos de protección respiratoria
(1)Respirador N95 con mascarilla de filtrado, con buen ajuste. Probado y aprobado por NIOSH, (2)Mascarilla
quirúrgica, no se ajusta a la cara y crea espacios por donde pueden entrar partículas. Autorizado por la FDA,
(3)Respirador N95 quirúrgico con mascarilla de filtrado, con buen ajuste y resistente a líquidos. Probado y
aprobado por NIOSH y autorizado por la FDA.
Los respiradores N95 con mascarilla de filtrado son una parte importante del control de infecciones
en los entornos de salud.

18
A diferencia de las mascarillas quirúrgicas, los respiradores están diseñados
específicamente para proporcionar protección respiratoria al crear un sello
hermético contra la piel y no permitir que pasen partículas que se encuentran
en el aire, entre ellas, patógenos. La designación N95 indica que el respirador filtra al menos
el 95% de las partículas que se encuentran en el aire. El personal debe usar los respiradores
conforme a las normas del programa integral de protección respiratoria OSHA 1940.134. Los
empleadores deben cumplir el requisito de crear e implementar un programa de protección
respiratoria escrito que incluya procedimientos específicos para el lugar de trabajo, y proveer
capacitación sobre esos procedimientos por parte de una persona calificada. La norma 1910.134
completa de la OSHA se puede encontrar en http://www.osha.govexternal icon (busque
“standard 1910.134“).
RESPIRADOR CON MASCARILLA DE FILTRADO
En la mayoría de los casos, en los entornos de salud, se usan los respiradores N95 aprobados por NIOSH con
mascarilla de filtrado para proteger a quienes los usan de las partículas en el aire, que incluyen patógenos. Tenga
en cuenta que los respiradores N95 no protegen contra gases, vapores o aerosoles y que podrían proporcionar
poca protección contra derrames directos de líquidos.
LAS MASCARILLAS QUIRÚRGICAS NO SON PROTECTORES RESPIRATORIOS
Las mascarillas quirúrgicas pueden ayudar a bloquear las gotitas más grandes de
partículas, derrames, aerosoles o salpicaduras, que podrían contener microbios,
virus y bacterias, para que no lleguen a la nariz o la boca. Sin embargo, se usan
principalmente para procurar proteger a los pacientes de los trabajadores de la
salud, reduciendo su exposición a saliva y secreciones respiratorias. No crean un
sello hermético contra la piel ni filtran los patógenos del aire muy pequeños, como
los que son responsables de enfermedades de transmisión aérea.

19
CESS Colson 2020
RESPIRADORES N95 QUIRÚRGICOS
Los respiradores N95 quirúrgicos proporcionan la protección respiratoria de los respiradores N95
y la protección contra aerosoles y salpicaduras de las mascarillas quirúrgicas. Estos productos están
aprobados por NIOSH como respiradores N95 y autorizados por la Administración de Alimentos y
Medicamentos (FDA) como dispositivos médicos.
¿Qué significa que algo cuenta con la aprobación de NIOSH?
Todos los respiradores que se usan en el entorno de la salud deben contar con la aprobación de
NIOSH, y son evaluados y probados minuciosamente por NIOSH para que cumplan con los estrictos
requisitos federales de seguridad. Para recibir la aprobación de NIOSH, los respiradores deben
cumplir con las normas de calidad y funcionamiento establecidas. Solamente entonces autorizará
NIOSH a que un fabricante de respiradores use el logo o el nombre de NIOSH en letras mayúsculas
en su producto. Los fabricantes deben contar con un programa de calidad establecido que asegure
que sus productos cumplen con los requisitos de NIOSH y deben mantener el programa
debidamente. Las marcas de aprobación de NIOSH en los respiradores con mascarilla de filtrado
pueden aparecer en la mascarilla misma o en las correas e incluir los elementos que se muestran a
continuación. Si un respirador con mascarilla de filtrado tiene marcas de aprobación, pero no
aparece en la tabla de NIOSH de respiradores con mascarilla de filtrado aprobados, es
probable que se trate de un producto falsificado o cuya certificación ha sido revocada o rescindida
por parte de NIOSH. Si no aparece un número que empiece con TC en el paquete del respirador, las
instrucciones para el usuario o el producto mismo, entonces no está aprobado por NIOSH. Si no está
seguro si su respirador cuenta con la aprobación de NIOSH, puede llamar a NIOSH al 412-386-4000.
Ejemplos de marcas externas en un respirador con mascarilla de filtrado aprobado por NIOSH
Número TC de aprobación de NIOSH: TC-84A-xxxx
Nombre de la marca, marca registrada o una abreviación que se reconozca fácilmente
El nombre NIOSH en letras mayúsculas o el logo de NIOSH
Clase de filtro (N, P o R) y el nivel de eficacia del filtro (95, 99 o 100)
Número de lote (se recomienda, pero no es obligatorio)
Número de modelo

20
Las apariencias pueden engañar Los empleadores tienen la obligación de proporcionar respiradores
aprobados por NIOSH a su personal cuando se necesite protección respiratoria. Los empleados
pueden ayudarlos verificando las marcas de NIOSH. No obstante, aun cuando las marcas
correspondientes parecen estar presentes, existen otras cosas que pueden afectar la seguridad.
DECLARACIÓN FALSA SOBRE EL NIVEL DE FILTRADO N95: Este producto no tenía las marcas
de NIOSH, pero estaba etiquetado con N95. Cuando se probó, no cumplió con los requisitos de rendimiento de filtrado
N95.
ALTERACIÓN NO AUTORIZADA, ANTES O DESPUÉS: Un respirador N95, cubierto con tela y
decorado con un diseño colorido, que anuló la certificación de NIOSH y puso en riesgo la seguridad de la persona que lo
usaba.
Anuncios engañosos: Respiradores con la aprobación de NIOSH falsificada y falsas declaraciones
Han aparecido en el mercado respiradores falsificados con el nombre o el logo de NIOSH. Los anuncian como respiradores
aprobados por NIOSH y con frecuencia se venden a precios bajos. La mejor defensa es verificar el número “TC” en la tabla
de NIOSH de mascarillas con filtrado
aprobadas https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/ y si tiene dudas comuníquese con
NIOSH al 412-386-4000.
Respiradores aprobados que han sido modificados o alterados o cuya aprobación de NIOSH ha sido revocada La
aprobación de NIOSH se aplica solamente al respirador, ya que ha sido probado y aprobado por esta entidad. Cualquier
modificación que se le haga a un respirador aprobado, incluso la más pequeña, puede afectar su forma, su funcionamiento,
la manera en que se ajusta a la cara y la protección que provee.
A continuación se describen algunas de las formas en que se modifican los respiradores y, por lo tanto, anulan la
aprobación de NIOSH:
El fabricante o un proveedor hace una modificación a un respirador sin darse cuenta del impacto que tiene el cambio o de la necesidad de hacer nuevas
pruebas y obtener nuevas aprobaciones (por ejemplo, si el fabricante cambia el modo en que se fijan las correas a la máscara).
Un tercero, no autorizado por NIOSH, le hace cambios a un respirador aprobado por NIOSH. Esto puede incluir el intento de copiar el producto aprobado.
La misma persona que usa un respirador lo modifica de alguna manera para que sea más cómodo o se vea mejor, y afecta su propia protección (por ejemplo,
si se le aplica un adorno al respirador aprobado para transformarlo en un objeto de moda).
Respiradores a los que se les revocó o rescindió la aprobación de NIOSH obtenida previamente que se vuelven a empaquetar y se venden con el nombre de
otra marca.
¿Cómo descubre NIOSH los respiradores falsificados o modificados?
NIOSH participa activamente en la identificación de respiradores falsificados y los que han sido aprobados y luego
modificados de alguna manera. NIOSH se entera por varios medios de estos productos que afectan su seguridad:
Fabricantes legítimos que denuncian a comerciantes que ponen en el mercado productos modificados
Fabricantes legítimos que denuncian la producción de copias piratas de sus propios productos
Usuarios que hacen consultas o dan informe
Anuncios de respiradores alterados
Anuncios de productos con etiquetas falsas o erróneas
El Programa de Aprobación de NIOSH realiza auditorías constantes, posteriores a la aprobación, de productos certificados
y sitios de fabricación autorizados.
Para NIOSH su salud y su seguridad son la primera prioridad. Debido a que su primera línea de defensa es el conocimiento,
nos hemos asegurado de que toda la información que necesita esté al alcance de su computadora.
Visite http://KnowIts.NIOSH.govexternal icon para acceder a información sobre respiradores, su uso y los
problemas que afectan el bienestar suyo y el de los pacientes que atiende.

22
Milton, D., M. Fabian, B. Cowling, M. Grantham y J.
McDevitt. 2013. Influenza virus aerosols in human exhaled
breath: particle size, culturability, and effect of surgical
masks. PLoS Pathog 9 (3): e1003205.
https://doi.org/10.1371/journal.ppat.1003205.
Abstract The CDC recommends that healthcare settings provide influenza patients with facemasks
as a means of reducing transmission to staff and other patients, and a recent report suggested that
surgical masks can capture influenza virus in large droplet spray. However, there is minimal data on
influenza virus aerosol shedding, the infectiousness of exhaled aerosols, and none on the impact of
facemasks on viral aerosol shedding from patients with seasonal influenza.We collected samples of
exhaled particles (one with and one without a facemask) in two size fractions (“coarse”>5 µm,
“fine”≤5 µm) from 37 volunteers within 5 days of seasonal influenza onset, measured viral copy
number using quantitative RT-PCR, and tested the fine-particle fraction for culturable virus.Fine
particles contained 8.8 (95% CI 4.1 to 19) fold more viral copies than did coarse particles. Surgical
masks reduced viral copy numbers in the fine fraction by 2.8 fold (95% CI 1.5 to 5.2) and in the coarse
fraction by 25 fold (95% CI 3.5 to 180). Overall, masks produced a 3.4 fold (95% CI 1.8 to 6.3)
reduction in viral aerosol shedding. Correlations between nasopharyngeal swab and the aerosol
fraction copy numbers were weak (r = 0.17, coarse; r = 0.29, fine fraction). Copy numbers in exhaled
breath declined rapidly with day after onset of illness. Two subjects with the highest copy numbers
gave culture positive fine particle samples.Surgical masks worn by patients reduce aerosols shedding of
virus. The abundance of viral copies in fine particle aerosols and evidence for their infectiousness suggests an
important role in seasonal influenza transmission. Monitoring exhaled virus aerosols will be important for
validation of experimental transmission studies in humans.
Author Summary The relative importance of direct and indirect contact, large droplet spray, and
aerosols as modes of influenza transmission is not known but is important in devising effective
interventions. Surgical facemasks worn by patients are recommended by the CDC as a means of
reducing the spread of influenza in healthcare facilities. We sought to determine the total number
of viral RNA copies present in exhaled breath and cough aerosols, whether the RNA copies in fine
particle aerosols represent infectious virus, and whether surgical facemasks reduce the amount of
virus shed into aerosols by people infected with seasonal influenza viruses. We found that total
viral copies detected by molecular methods were 8.8 times more numerous in fine (≤5 µm)
than in coarse (>5 µm) aerosol particles and that the fine particles from cases with the
highest total number of viral RNA copies contained infectious virus. Surgical masks reduced
the overall number of RNA copies by 3.4 fold. These results suggest an important role for aerosols
in transmission of influenza virus and that surgical facemasks worn by infected persons are
potentially an effective means of limiting the spread of influenza.

23
CESS Colson 2020
Mniszewski, Susan, Sara Del Valle, Reid Priedhorsky, James
Hyman y Kyle Hickman. 2013. Understanding the impact of
face mask usage through epidemic simulation of large
social networks. En Theories and Simulations of Complex
Social Systems, pp 97-115.
27 October 2013 Part of the Intelligent Systems Reference Library book series (ISRL, volume 52)
Abstract
Evidence from the 2003 SARS epidemic and 2009 H1N1 pandemic shows that face masks
can be an effective non-pharmaceutical intervention in minimizing the spread of airborne
viruses. Recent studies have shown that using face masks is correlated to an individual’s
age and gender, where females and older adults are more likely to
wear a mask than males or youths. There are only a few studies quantifying
the impact of using face masks to slow the spread of an epidemic at the population level,
and even fewer studies that model their impact in a population where the use of face masks
depends upon the age and gender of the population. We use a state-of-the-art agent-based
simulation to model the use of face masks and quantify their impact on three levels of an
influenza epidemic and compare different mitigation scenarios. These scenarios involve
changing the demographics of mask usage, the adoption of mask usage in relation to a
perceived threat level, and the combination of masks with other non-pharmaceutical
interventions such as hand washing and social distancing. Our results shows that face
masks alone have limited impact on the spread of
influenza. However, when face masks are combined
with other interventions such as hand sanitizer, they
can be more effective. We also observe that monitoring social internet
systems can be a useful technique to measure compliance. We conclude that educating the
public on the effectiveness of masks to increase compliance can reduce morbidity and
mortality.
1 Introduction

24
Pharmaceutical interventions such as vaccines and antiviral medication are the best
defense in reducing morbidity and mortality during an influenza pandemic. However,
current egg-based vaccine production process can take up to 6 months for the development
and availability of a strain-specific vaccine and antiviral supplies may be limited.
Fortunately, alternative strategies such as non-pharmaceutical interventions can reduce
the spread of influenza until a vaccine becomes available. Face masks have been used to
combat airborne viruses such as the 1918–1919 pandemic influenza [4, 29], the
2003 SARS outbreak [7, 38], and the most recent 2009 H1N1 pandemic [12]. These
studies indicate that if face masks are readily available, then they may be more cost-
effective than other non-pharmaceutical interventions such as school and/or
business closures [13]. We focus on the use of surgical face masks and N95 respirators
(also referred to as face masks). A surgical mask is a loose-fitting, disposable device that
prevents the release of potential contaminants from the user into their immediate
environment [8, 40]. They are designed primarily to prevent disease transmission to others,
but can also be used to prevent the wearer from becoming infected. If worn properly, a
surgical mask can help block large-particle droplets, splashes, sprays, or splatter that may
contain germs (viruses and bacteria), and may also help reduce exposure of saliva and
respiratory secretions to others. By design, they do not filter or block very small particles in
the air that may be transmitted by coughs or sneezes.
An N95 respirator is a protective face mask designed to achieve a very close facial fit and
efficient filtration of airborne particles [40]. N95 respirators are designed to reduce an
individual’s exposure to airborne contaminants, such as infectious viral and bacterial
particles, but they are also used to prevent disease transmission when worn by a sick
individual [20]. Typically, they are not as comfortable to use as a surgical face mask, and
some health care workers have found them difficult to tolerate [23]. N95 respirators are
designed for adults, not for children, and this limits their use in the general population.
Surgical masks and N95 respirators have been found to be equally effective in preventing
the spread of influenza in a laboratory setting [20] as well as for health care workers [24].
In addition to reducing the direct flow of an airborne pathogen into the respiratory system
the masks act as a barrier between a person’s hands and face, which can reduce direct
transmission. A survey paper by Bish and Michie [5] on demographic determinants of
protective behavior showed that compliance to using face masks is tied to age and gender.
They observed that females and older adults were more likely to accept protective behaviors
than other population groups. Supporting these ideas, usage of face masks was consistently
higher among females than male metro passengers in Mexico City during the 2009
Influenza A (H1N1) pandemic [12]. Limited studies suggest that there is more social
stigmatization associated with wearing face masks in Western Countries than in Asia. For
example, people rarely wear face masks in public in the United States, compared with their
use in Japan and China [17]. An article published in 2009 by New York Times
Health reported that “masks scare people away from one another” resulting in an
unintentional social distancing measure [30] or “stay away” factor. Pang et al. showed that
during the 2003 SARS outbreak, non-pharmaceutical interventions where implemented
followed the epidemic curve [33]. That is, as the perception of SARS increased, more
measures were implemented, and as the incidence declined, several measures were relaxed.
Based on these studies, we investigate the impact of face mask usage on the spread of
influenza under several assumptions, including: (1) that females and older people will be
more likely to wear them, (2) face mask wearers may follow the epidemic (e.g., the number
of people wearing face masks depends on the incidence), and (3) face masks scare people
away. In order to transfer our results to the real world, it will be important to measure
compliance. In the case of interventions such as face mask use, where individuals often

25
CESS Colson 2020
choose to comply or not comply in the privacy of their daily lives, traditional methods of
measuring compliance may be ineffective. Accordingly, we turn to social internet systems,
specifically Twitter, where users share short text messages called tweets. These messages
are directed to varying audiences but are generally available to the public regardless; they
are used to share feelings, interests, observations, desires, concerns, and the general chatter
of daily life. While other researchers have used Twitter to measure public interest in various
health topics, including face masks as an influenza intervention [35], we carry out a brief
experiment to explore the feasibility of using tweets to measure behavior. The goal of this
study is to understand the effectiveness of face mask usage for influenza epidemics of
varying strengths (high, medium, low). A high level epidemic would be similar to the 1918–
1919 H1N1 “Spanish flu” outbreak with large morbidity and mortality [32, 34, 42], a
medium level would be similar to the 1957–1958 H2N2 Asian flu [15, 18], and a low level
would be similar to the more recent 2009 Novel H1N1 flu [6, 10, 19]. We simulate face mask
usage behavior through detailed large-scale agent-based simulations of social networks.
These simulations have been performed using the Epidemic Simulation System (EpiSimS)
[27, 28, 37] described in the next section.
2 Methods
2.1 Agent-Based Model Description
EpiSimS is an agent-based model that combines three different sets of information to
simulate disease spread within a city: population (e.g., demographics),locations (e.g.,
building type and location), andmovement of individuals between locations (e.g.,
itineraries). We simulated the spread of an influenza epidemic in southern California with
a synthetic population constructed to statistically match the 2000 population
demographics of southern California at the census tract level. The synthetic population
consists of 20 million individuals living in 6 million households, with an additional 1 million
locations representing actual schools, businesses, shops, or social recreation addresses. The
synthetic population of southern California represents only individuals reported as
household residents in the 2000 U.S. Census; therefore, the simulation ignores visiting
tourists and does not explicitly treat guests in hotels or travelers in airports.We use the
National Household Transportation Survey (NHTS) [44] to assign a schedule of activities
to each individual in the simulation. Each individual’s schedule specifies the starting and
ending time, the type, and the location of each assigned activity. Information about the
time, duration, and location of activities is obtained from the NHTS. There are five types of
activities: home, work, shopping, social recreation, and school, plus a sixth activity
designated other. The time, duration, and location of activities determines which
individuals are together at the same location at the same time, which is relevant for airborne
transmission.
Each location is geographically-located using the Dun and Bradstreet commercial database
and each building is subdivided based on the number of activities available at that location.
Each building is further subdivided into rooms or mixing places. Schools have classrooms,
work places have workrooms, and shopping malls have shops. Typical room sizes can be
specified; for example, for workplaces, the mean workgroup size varies by standard
industry classification (SIC) code. The number of sub-locations at each location is
computed by dividing the location’s peak occupancy by the appropriate mixing group size.
We used two data sources to estimate the mean workgroup by SIC, including a study on
employment density [45] and a study on commercial building usage from the Department
of Energy [26]. The mean workgroup size was computed as the average from the two data
sources (normalizing the worker density data) and ranges from 3.1 people for

26
transportation workers to 25.4 for health service workers. The average over all types of work
is 15.3 workers per workgroup. For the analyses presented here, the average mixing group
sizes are: 8.5 people at a school, 4.4 at a shop, and 3.5 at a social recreation venue.
2.2 Disease Progression Model
Airborne diseases spread primarily from person-to-person during close proximity through contact,
sneezing, coughing, or via fomites. In EpiSimS, an interaction between two individuals is
represented only by:when they begin to occupy a mixing location together,
how long they co-occupy within a mixing place,a high-level description of the activity they are
engaged in, andthe ages of the two individuals.A location represents a street address, and a room or
mixing place represents a lower-level place where people have face-to-face interactions. When an
infectious person is in a mixing location with a susceptible person for some time, we estimate a
probability of disease transmission, which depends on the last three variables listed above. Details
of social interactions such as breathing, ventilation, fomites, moving around within a sub-location,
coughing, sneezing, and conversation are not included. Disease transmission between patients and
medical personnel is not handled explicitly, and no transmission occurs when traveling between
activities. Note that individuals follow a static itinerary, except when they are sick or need to care for
a sick child. In this case, their schedule changes and all activities they were supposed to undertake
are changed to home.If susceptible person jj has a dimensionless susceptibility multiplier SjSj,
infectious person II has an infectious multiplier IiIi and TT is the average transmissibility per unit
time, then, TSjIiTSjIi will be the mean number of transmission events per unit time between fully
infectious and fully susceptible people. The sum
∑jTSjIi∑jTSjIi extends over all infectious persons that co-occupied the room with individual jj.
For events that occur randomly in time, the number of occurrences in a period of time of
length tt obeys a Poisson probability law with parameter.
∑jTSjIit∑jTSjIit Thus, the probability of no occurrences in time interval tt is
e−∑jTSjIite−∑jTSjIit
and the probability of at least one occurrence is
1−e−∑jTSjIit1−e−∑jTSjIit
Using the mean duration tijtij of contacts between a susceptible person jj and infectious person ii,
we assume that the probability that susceptible individual jj gets infected during an activity is
computed as:
Pj=1−e−∑jTSjIitijPj=1−e−∑jTSjIitij
(1)
Disease progression is modeled as a Markov chain consisting of five main epidemiological
stages: uninfected, latent (non-infectious), incubation (partially infectious), symptomatic
(infectious), and recovered. The incubation and symptomatic stage sojourn time distributions are
described by a half-day histogram, giving respectively the fraction of cases that incubate for a period
of between 0 and 0.5 days, 0.5 and 1.0 days, etc., before transitioning to the symptomatic or
recovered stages, respectively. The average incubation time is 1.9 days and average duration of
symptoms is 4.1 [25]. The influenza model assumes that 50 % of adults and seniors, 75 % of students,
and 80 % of pre-schoolers will stay at home soon within 12 hrs of the onset of influenza symptoms.
These people can then transmit disease only to household members or visitors. In addition, based
on previous studies [25], we assume that 33.3 % of infections are subclinical
where an infected individual is asymptomatic and shows no sign of infection. We modeled the
subclinical manifestation as only half as infectious as the symptomatic manifestations. Persons with
subclinical manifestations continue their normal activities as if they were not infected. The assumed
hospitalization rate is a percentage of symptomatic individuals dependent on the strength of the
pandemic. To simulate the higher attack rates seen in children, we assume that the infection rate in
children was double that in adults. We analyze multiple scenarios for the same set of transmission

27
CESS Colson 2020
parameters where the population was initially seeded with 100 people infected, all in the incubation
stage.
2.3 Behavior Model The behavior of each individual (agent) in an EpiSimS simulation is
defined based on distributions for the effectiveness of their face mask usage in preventing
infection to others (given as a distribution), effectiveness to preventing the individual from
becoming infected (given as a distribution), acceptance of using the mask (given as a
distribution), along with applicable age range, gender, and other possible demographic
descriptive information. Effectiveness to others for mask usage is based on the protection
factor of a mask type. It is the protection provided to people in contact with a sick individual
wearing a mask. Effectiveness to self is based on the penetration level of a mask type. It is
the protection provided to a healthy individual when in close contact with an infectious
person. Distributions were used based on mask testing for the penetration level
[2, 9, 21, 31] and protection factor [22]. Examples of these distributions are shown for N95
respirators in Table 1 and for surgical masks in Table 2. The effectiveness values drawn
from each distribution are used to modify the infectivity (IiIi) and susceptibility (SjSj)
between pairs contributing to whether or not transmission occurs.
Table 1 Effectiveness of N95 respirators in preventing an infected person from
infecting others (protection factor) and the effectiveness of the face mask to
prevent the wearer from being infected (penetration level) are listed along
with the percentage of face mask users with this level of effectiveness from
testing
Effectiveness to
others
N95 respirator
(%)
Effectiveness to
self
N95
(%)
(protection factor) users (penetration level) users
less than 0.1 0.00 less than 0.5 9.52
0.1 87.88 0.5 9.52
0.5 12.12 0.6 14.29
0.7 14.29
0.8 33.33
0.9 19.05

28
Table 2
Effectiveness of surgical masks in preventing an infected person from infecting others
(protection factor) and the effectiveness of the face mask to prevent the wearer from being
infected (penetration level) are listed along with the percentage of face mask users with this
level of effectiveness from testing
Effectiveness to
others
Surgical mask
(%)
Effectiveness to
self
Surgical mask
(%)
(protection factor) users (penetration
level)
users
<0.1<0.1 91.67 0.1 13.89
0.1 8.33 0.2 8.33
0.3 5.55
0.5 5.55
0.6 11.12
0.7 38.89
0.8 16.67
As stated previously, age and gender play an important role in determining whether
someone will comply with wearing a mask. The age ranges and compliance or acceptance
by gender are based on values from a survey of behavior studies [5] and are shown in
Table 3. Simulations that assigned mask usage by age and gender used the age ranges and
acceptance in this table. Simulations that assigned mask usage randomly used constant
acceptance values (e.g., 25 % of the population) for adults-only or all.

29
CESS Colson 2020
Table 3 Face mask acceptance by gender and age. Notice that the willingness to use a
face mask increases with age and that women are more willing to use a face mask than men
of the same age
Age group Males (%) Females
(%)
6–15 33 33
16–24 33 54
25–34 45 63
35–44 59 74
45–54 55 68
55–64 59 71
65–74 63 75
75+ 57 72
Average 57 64
We assume that willingness to wear a mask is not influenced by a person being ill and the
masks are only worn in non-home settings. Mask usage is initiated as an exogenous event,
specified for a range of days. Usage can be specified as a fraction of all possible users (based
on age and gender) and the duration can be specified as a distribution (e.g., constant,
normal). Early in the simulations, each individual determines whether they will wear a
mask based on age, gender, and acceptance. This is the pool of people from which mask
users are selected. When we assume that mask usage will follow the course of an epidemic
(e.g., disease perception increases as incidence increases and vice-versa), mask usage
ramps up and then down. For this scenario, mask users change over time and some may
use masks for a sequence of days multiple times.Scenarios that take into account a stay
away factor used higher effectiveness values based on assumptions regarding the amount
of social distancing we expect a mask wearer to experience (e.g., 30 %). The mechanism we
are assuming here is that, in general, individuals will attempt to limit their contact with a
person wearing a mask. This translates to a larger histogram bin size for the distribution.
Scenarios where both surgical masks and hand sanitizer served as the mitigation strategy,
do not use the protection level and penetration factor values for effectiveness as described
previously, instead an effectiveness value of 50 % is used based on an intervention trial
conducted at the University of Michigan [1].
2.4 The Reproduction Number
In epidemiological models, the effectiveness of mitigation strategies are often measured by
their ability to reduce the effective reproduction number or replacement
number ReffReff. ReffReff is the average number of secondary cases produced by a typical
infectious individual during their infectious period [46]. In a completely susceptible
population and in the absence of mitigation strategies, the average number of secondary

30
cases is referred to as R0R0. The magnitude of R0R0 determines whether or not an
epidemic will occur and if so, its severity. The number of infections grows when R0R0 is
greater than one and it dies out when R0R0 is less than one.
3 Results We compare a base case scenario where no face masks are used for the high,
medium, and low epidemic levels with simulations using only face masks, face masks and
hand sanitizer (M and HS), and face masks coupled with social distancing (M and SD). For
the base case scenarios, we compare the epidemic parameters related to morbidity and
mortality, including the attack rate, clinical attack rate, hospitalization rate, and mortality
rate. All of the scenarios that include face mask usage mitigations allow mask base
acceptance by age and gender. Additionally, mask users follow the course of the epidemic
incidence, increasing to the peak and then decreasing, ending 4 weeks after the peak. In
support of this behavior, we present the results of a small experiment, where we use Twitter
to estimate the shape of the compliance curve with respect to face masks.Surgical
masks and N95 respirators are considered independently in
the face mask only scenarios, while surgical masks are the
choice for the hand sanitizer and social distancing scenarios.
N95 respirators can be more effective if both adults and children would use them, but they
have not been designed for children and can be uncomfortable even for adults for long-term
use. For these scenarios where mitigations are implemented, we compare the clinical attack
rate, effective reproductive number, and for some cases, we show the the disease prevalence
(symptomatic cases), incidence of mask users (new cases), and the effective reproductive
number over time (ReffReff).
3.1 Base Case Scenario
As described earlier, we used influenza epidemics of varying strengths (high, medium, low)
to compare the impact of face mask usage on controlling the spread. These different levels
share a similar disease progression as described in Sect. 2. The high level epidemic is based
on the 1918–1919 H1N1 “Spanish flu” outbreak and has large morbidity and mortality
[32, 34, 42], the medium level is based on the 1957–1958 H2N2 Asian flu [15, 18], and the
low level is based on the more recent 2009 Novel H1N1 flu [6, 10, 19]. The number of
hospitalizations and deaths were extrapolated from the U.S. population during the
represented pandemic year to the U.S. synthetic population of 280M (based on 2000
census data). The attack rate (percentage of population infected), clinical attack rate
(percentage of population symptomatic), hospital rate (hospitalizations out of population),
and mortality rate (deaths out of population) are shown for each strength in Table 4.
Figure 1 shows each of their respective epidemic curves for the new symptomatic as a
function of time.

31
CESS Colson 2020
Table 4
Epidemic parameters associated with high, medium, and low strengths of epidemic
Epidemic Attack rate Clinical attack Hospital rate Mortality rate
level (%) rate (%) (%) (%)
High 40.0 30.0 0.500 0.300
Medium 30.0 19.7 0.250 0.100
Low 20.0 10.0 0.008 0.015
3.2 Using Twitter to Quantify Face Mask Usage
Our goal in exploring Twitter is to evaluate two conjectures: first, that the level of face mask
wearing follows the disease incidence level, and second, that analysis of the public tweet
stream is a feasible technique to measure compliance with face mask wearing (and, by
implication, other behaviors relevant to infectious disease). To do so, we analyzed tweets
published globally between September 6, 2009 and May 1, 2010, roughly corresponding to
the H1N1 pandemic flu season in the United States.
Open image in new window
Fig. 1
Base case simulation results for the three different epidemic strengths, showing the
percentage of the population that becomes symptomatic per day
There are 548,893,258 tweets in our dataset, an approximate 10 % sample of total Twitter
traffic during this period. Of these, we selected the 75,946 which contained the word

32
“mask”; in turn, a small fraction of these keyword matches—we estimate 3,350, or about
4.5 %—actually concern the medical face masks of interest to the present work (topics also
include costume, sports, metaphor, cosmetics, movies, and others).
In order to identify these relevant tweets, we manually examined a random sample of 7,602
keyword matches (roughly 10 % of the total), coding them as (a) mentioning medical face
masks (335 tweets), and perhaps additionally (b) sharing a specific observation that either
the speaker or someone else is wearing, or has recently worn, a face mask (138 tweets).
Our results are shown in Fig. 2. As noted above, there are very limited survey studies that
have collected information on mask use, especially from Western Countries [5];
accordingly, we compare our Twitter mention and observation counts against influenza-
like illness (ILI) data published by the Centers for Disease Control (CDC) [11]. The
correlation is excellent: 0.92 for mentions and 0.90 for observations.
Fig. 2
Of each million tweets during the period September 6, 2009 through May 6, 2010, we show
the number in which face masks are mentioned, as well as the subset of mentions which
observe that someone specific is or was recently wearing a mask, whether the speaker
himself or someone else. Also shown is the influenza-like illness rate from the CDC for the
same period. The Pearson correlation between ILI rate and mentions is 0.92, and between
ILI rate and observations is 0.90
These results have two implications. They provide empirical support for our assumption
that face mask use is disease-dependent; that is, as disease incidence increases, face mask
use increases, and as incidence decreases, so does mask use. Also, they suggest more
broadly that social internet systems such as Twitter can, in fact, be used to measure disease-
relevant behavior in the real world.
Challenges remain, however. First, we point out the severe signal-to-noise of these data: we
identified just 20 out of every million tweets as relevant, even at the peak of the epidemic.
Accordingly, analysis focusing on specific locales or demographic groups is not possible
with this approach. Second, our manual coding approach clearly does not scale. Finally, we
strongly suspect that information relevant to our specific questions (e.g., How many people
are using face masks? Who are they? Where are they?) is contained in the vast number of
tweets our coarse, preliminary approach discards as irrelevant. Our future work in

33
CESS Colson 2020
measuring real-world behavior will go beyond simple keyword searches to leverage more
sophisticated data mining algorithms.
3.3 Comparison of Intervention Strategies
Face mask only mitigation strategies were considered for surgical masks and N95
respirators separately. All scenarios began when 0.01 or 1.0 % of the population was
symptomatic. Usage was based on age and gender and followed the course of the epidemic.
Surgical masks were available to all age groups and N95 respirators to adults only and all
age groups. Since N95 respirators were not designed for use by children, the adults only
scenario is more realistic; however the all age groups scenario allows us to understand the
importance of children wearing masks and the use of a more protective mask.Scenarios
with face mask usage starting when 1.0 % of the population was symptomatic resulted in
higher attack rates and clinical attack rates than that for 0.01 % and will not be considered
further here. Those starting at 0.01 % slowed the epidemic, allowing less burden to the
public health system.Table 5 shows the overall clinical attack rates for the epidemic as well
as just for the mask users for all scenarios and epidemic strengths. Overall, only a small
improvement is seen over the base case. The maximum mask users for all scenarios is 45–
50 % of the population. Considering only the mask users, the clinical attack rates are much
improved, with significant reductions for all three scenarios. The largest improvement is
seen for N95 respirator where use is not limited to adults. This shows the importance of
involving children in a face mask mitigation. Of the more realistic scenarios, surgical mask
and N95 respirator adults, surgical mask performs best overall for all pandemic strengths,
though worst when only considering mask users.
Table 5
Attack rate parameters associated with high, medium, and low strengths of epidemic for
face mask only scenarios starting when 0.01 % of the population is symptomatic
Epidemic Mask Attack
rate
Overall Mask users
level scenario (%) Clinical
attack
Clinical
attack
rate (%) rate (%)
High Surgical mask 34.22 25.66 14.24
N95 respirator
adults
35.03 26.27 12.74
N95 respirator all 32.26 24.20 12.09
Medium Surgical mask 24.51 16.35 7.40
N95 respirator
adults
25.55 17.04 7.03
N95 respirator all 23.40 15.60 5.89

34
Epidemic Mask Attack
rate
Overall Mask users
level scenario (%) Clinical
attack
Clinical
attack
rate (%) rate (%)
Low Surgical Mask 16.35 8.18 2.88
N95 Respirator
Adults
17.69 8.85 2.80
N95 Respirator All 16.96 8.49 1.73
We compare the impact of combining face masks with hand sanitizers (M and HS) or with
social distancing (M and SD). As described in Sect. 2.3, M and HS are assumed to reduce
the transmission rate by 50 % and M and SD are assumed to reduced the transmission rate
by 30 %. Figure 3, part A and C shows the epidemic curves when M and HS are
implemented after 1.0 % of the population is symptomatic, and M and SD when 0.01 % of
the population is symptomatic, respectively. In addition to showing the overall dynamics of
these two interventions, we show the epidemic curve for individuals who adopted the
specified behavior, but who still became infected. Note that although the clinical attack rate
was only reduced by 19 and 21 % for these two scenarios, the clinical attack rate for M and
HS users was only 3.6 or an 81 % reduction. Similarly, the clinical attack rate for the M and
SD users is 4.7 or a 76 % reduction from the base case. Part B and D, shows the clinical
attack rate for various assumptions of the M and HS and M and SD scenarios and all the
different pandemic levels.

35
CESS Colson 2020
Fig. 3
Results of surgical masks and hand sanitizers (top) and masks and social distancing
(bottom). a Epidemic curves for the base case, when the intervention is implemented after
1.0 % of the population is symptomatic, and the population that adopts the behavior (M
and HS users). b Clinical attack rates (CAR) for the various pandemic levels and when
masks and hand sanitizers are implemented after 1.0 and 0.01 % of the population is
symptomatic. c Epidemic curves for the base case, when the intervention is implemented
after 0.01 % of the population is symptomatic, and the population that adopts the behavior
(M and SD users). d Clinical attack rates (CAR) for the base case, and two mask and social
distancing scenarios for the different pandemic levelsFrom the results, it is clear that the
earlier the interventions are put in place, the higher the impact they will have on reducing
morbidity and mortality. Although these non-pharmaceutical interventions may not be very
effective when compared to vaccines and antivirals, the overall impact for people that adopt
these behaviors is significantly lower than the epidemic curve for the entire population.
Table 6 takes the new clinical attack rate for the M and HS and M and SD intervention
strategies and computes their difference. Then, this difference is expressed in the table as a
percentage of the base case clinical attack rate for that epidemic strength. This is meant to
demonstrate the difference in the clinical attack rate relative to each intervention strategy
on a scale that is proportional to the base case. If this percent is small then one could
reasonably conclude that there is not much difference in the intervention strategies at that
level. Overall, the scenarios with masks and hand sanitizer had a difference of less than
10 % of the base case clinical attack rate in all cases (see Table 7). The case of comparing M
and HS implemented when 0.01 % of the population is symptomatic and M and SD when
1.0 % of the population is symptomatic is especially interesting at a low epidemic level, since
the difference is less than 5 % even though M and SD has only a 30 % effectiveness
compared to M and HS 50 % effectiveness. This motivates future studies into the difference
in the effectiveness of these two intervention strategies at various epidemic strengths.
Table 6
Difference in clinical attack rate as a percent of base case clinical attack rate when
comparing M and SD and M and HS intervention strategies
R0R0 0.01 M and
HS (%)
1.00 M and
HS (%)
1.00 M and
HS (%)
0.01 M and
HS (%)
0.01 M and
SD (%)
1.00 M and
SD (%)
0.01 M and
SD (%)
1.00 M and
SD (%)
1.10 3.60 1.00 3.00 0.40
1.38 0.51 4.10 2.60 6.12
1.66 3.00 2.00 1.70 6.70

36
Table 7
Percent reduction in clinical attack rate from base case at different epidemic strengths for
M and HS or M and SD implemented at different epidemic levels
R0R0 M and HS M and SD
0.01 (%) 1.00 (%) 0.01 (%) 1.00 (%)
1.10 16.40 17.00 20.00 16.00
1.38 20.90 18.90 21.40 14.80
1.66 21.30 16.70 18.30 14.67
Note that at low epidemic levels, if implemented early, social distancing is competitive with
hand sanitizing as an intervention strategy
To better understand the overall effectiveness of the different intervention strategies we
compare the effective reproduction number, ReffReff, for five different scenarios:
Surgical mask only (Mask),
N95 respirators only-adults (N95 Adult),
N95 respirators only-all (N95 All),
Surgical masks and social distancing (Mask and Social Distancing), and
Surgical masks and hand sanitizer (Mask and Hand Sanitizer).
All scenarios assume that the intervention begins when 0.01%0.01% of the population is
symptomatic, follows the course of the epidemic (ramping up to the peak and then down),
and lasts 4 weeks after the peak. The likelihood of use of a non-pharmaceutical
intervention, in each scenario, was dependent on age and gender as discussed previously.
Fig. 4
ReffReff over time as the epidemic progresses. For five different scenarios (shown starting
from day 40), the dynamic behavior of ReffReff is different. Intervention strategies cause

37
CESS Colson 2020
the initial ReffReff to be smaller than the base case, and then take longer to decrease
below Reff=1Reff=1. (The N95 Adult case has an initially higher ReffReff than the other
scenarios, presumably since children did not have intervention in this case.)
Figure 4 shows the change in the effective reproduction number, ReffReff, over the course
of the epidemic for the five scenarios described above during a medium (R0R0 = 1.38) level
outbreak. The basic reproduction number, R0R0, is the average number of cases generated
by a typical infectious individual in a completely susceptible population. Similarly, the
effective reproduction number is the average number of cases generated by an infectious
individual in a population that is not completely susceptible. The magnitude of the
reproduction number determines whether or not an epidemic occurs and what its severity
will be. When R0>1R0>1, the number of infections grow and an epidemic occurs, and
when R0<1R0<1, the epidemic goes extinct.
We notice (Fig. 4) that for the different intervention strategies, the maximum ReffReff is
reduced. The exception is for the N95 scenario, N95 Adult, when children do not wear
masks. In this case, ReffReff shows a dramatic decrease but starts out high; this exception
is not present if children wear the respirators as in N95 All.
4 Discussion
Non-pharmaceutical interventions such as face masks can play an
important role in controlling the spread of airborne viruses. Based on
historical observations, it is clear that some people wear face masks to protect themselves
from infection. However, due to their limited effectiveness (known from filtration
performance tests) the impact of face masks at the population level has not been well
studied. We used an agent-based simulation model to examine the effect that face masks
alone, and in combination with other non-pharmaceutical interventions, has on reducing
the spread of influenza. We analyzed the sensitivity with respect to various parameters
including pandemic level, type of face mask, timing of intervention(s), and type of
intervention. Our results show that, in general, face masks have an impact on reducing the
overall incidence and extending the length of the epidemic. Masks alone reduce
the clinical attack rate, on average, by over 10 % for the entire
population and 50 % for the population that wears face masks.
Not surprisingly, our results show that face masks are more effective when coupled with
other interventions. Although we expected that masks and hand sanitizers would have the
largest return (given that we assume to be 50 % effective), social distancing performed
almost as well as the hand sanitizer (even though we assume it was only 30 % effective).
These observations imply that any mitigation that aims at reducing the probability of
transmission, regardless of effectiveness, can contribute in reducing the overall impact of
disease. Furthermore, the results are consistent with other studies concluding that the
earlier interventions are put in place, the higher the impact they have on reducing morbidity
and mortality.
We compare the effective reproduction numbers for various scenarios and show that
intervention strategies cause the initial ReffReff to be smaller than the base case and take
longer to decrease below ReffReff = 1. We also noted that the N95 case had an initially
higher ReffReff than the other scenarios due to the assumption that children would not

38
wear N95 respirators. For any intervention, it is important to measure the rate at which the
intervention is actually happening. Non-pharmaceutical interventions such as face mask
wearing presents special problems in this regard, because the decision to comply or not
comply is an individual one which takes place away from observation by health providers.
The intuition in exploring social internet systems such as Twitter to make these
measurements is that the very high volume of observations, perceptions, and desires can,
in aggregate, provide a sufficiently accurate measurement of compliance in real-world
settings. Our preliminary results in analyzing Twitter are consistent with this intuition: we
measured the use of face masks with a simple keyword-based approach, and both mentions
of and observations of wearing face masks correlate strongly with CDC influenza incidence
data. We expect future efforts to deepen this capability, providing results segmented by
locale or demographics.
We conclude that for mathematical models of infectious diseases to be useful in guiding
public health policy, they need to consider the impact of non-pharmaceutical interventions.
Face masks can be a cost-effective intervention when
compared to closures; therefore, public health
campaigns should focus on increasing compliance.
Additionally, measuring the effect of these campaigns should include analysis of social
internet systems and other emerging data sources. The results presented here are useful in
providing estimates of the effects of non-pharmaceutical interventions on the spread of
influenza.
References
1.Aiello, A.E., Perez, V., Coulborn, R.M., et al.: Facemasks, hand hygiene, and influenza among
young adults: a randomized intervention trial. PLoS One 7(1), e29744 (2012)CrossRefGoogle
Scholar
2.Balazy, A., Toivola, M., Adhikari, A. et al.: Do N95 respirators provide 95% protection level against
airborne virus, and how adequate are surgical masks? Am. J. Infect. Control 34(2), 51–57
(2006)Google Scholar
3.Barr, M., Raphael, B., Taylor, M. et al.: Pandemic influenza in Australia: using telephone surveys
to measure perceptions of threat and willingness to comply. BMC Infect. Dis. 8, 117 (2008)Google
Scholar
4.Billings, M.: The influenza pandemic of 1918: the public health
response. http://virus.stanford.edu/uda/fluresponse.html (2005). Accessed 26 April 2012
5.
Bish, A., Michie, S.: Demographic and attitudinal determinants of protective behaviours during a
pandemic: a review. Br. J. Health Psych. 15, 797–824 (2010)CrossRefGoogle Scholar
6.Bronze, M.S.: H1N1 influenza (swine flu). Medscape
reference. http://emedicine.medscape.com/article/1807048-overview (2012). Accessed 27 April
2012
7.Brookes, T., Khan, O.A.: Behind the mask: how the world survived SARS, the first epidemic of the
twenty-first century. American Public Health Association, Washington, DC (2005)Google Scholar
8.
Brosseau, L., Ann, R.B.: N95 respirators and surgical masks. http://blogs.cdc.gov/niosh-science-
blog/2009/10/n95/ (2012). Accessed 11 May 2012
9.Centers for Disease Control and Prevention: Laboratory performance evaluation of N95 filtering
respirators,
1996. http://www.cdc.gov/mmwr/preview/mmwrhtml/00055954.htm#00003611.htm (1998).
Accessed 26 April 2012
10.Centers for Disease Control and Prevention: CDC estimates of 2009 H1N1 influenza cases,
hospitalizations and deaths in the United States, April 2009–January 16,

Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19.

Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19.

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19.

Similar to Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19. (20)

More from JESUS HARO ENCINAS

More from JESUS HARO ENCINAS (20)

Recently uploaded

Recently uploaded (20)

Haro 2020 dossier cubrebocas y mascarillas protectoras en la pandemia covid 19.