Are Masks Worth the Trouble?
By now many people know that I am researching bird flu issues and I get more and more questions about whether, when, or how to prepare for a possible outbreak -- for example, whether it makes sense to buy face masks.
You may have seen pictures from 1918 of people wearing face masks covering mouth and nose, a practice that today is far more prevalent during flu season in Asia than here. Do they know something we don’t?
What are the official recommendations on masks?
WHO recommends that health-care workers who will be within 3 feet (1 metre) of infected patients use medical masks (e.g., surgical or procedure) when caring for patients either with, or suspected to have, pandemic influenza. For simplicity, health-care facilities also may recommend that health-care workers use such masks whenever entering a room containing a patient diagnosed with pandemic influenza. (WHO, 2005a)[1]
Hmmm -- no mention of masks for those who are not “health-care workers”? Is this an omission? Maybe not:
“Mask wearing by the general population is not expected to have an appreciable impact on transmission, but should be permitted, as this is likely to occur spontaneously.” (WHO, 2005b)[2]
So, masks are expected to have an appreciable effect in protecting health-care workers, but not in protecting the general public? What does the Department of Health and Human Services (DHHS) have to say about masks in its “Pandemic Influenza Planning: A Guide for Individuals and Families”[3]? Well – apparently nothing.
How about the more extensive DHHS “Pandemic preparedness plan” of November 2005?
“The benefit of wearing masks by well persons in public settings has not been established and is not recommended as a public health control measure at this time.” (p. S8-11)
Of course, persons with symptoms of respiratory infections are encouraged to wear masks: (CDC flyer)[4]
“CDC does not recommend the routine use of personal protective equipment (PPE), such as respirators, gloves, or surgical masks, for protection against avian influenza exposure, except in health care-related situations.” (CDC, 2006)[5]
HUH?
Are we to believe that masks stop virus-laden particles only when they are outgoing? Are we further to believe that masks can protect against incoming virus-laden particles, but only in “health care-related situations”? How would a virus or a droplet know the difference?
Is there really no evidence?
The typical claim is that there is no evidence that masks are effective against influenza virus transmission. That sounds to me like the official recommendations confuse absence of evidence with evidence of absence.
True, there are no controlled studies on influenza, but at least two studies find that wearing face masks gives significant protection against SARS.[6],[7],[8] Why would masks provide significant protection against SARS but not influenza? I don’t believe it’s the species of virus that matters.
Size matters:
Influenza virus particles are only 0.25 micrometers in diameter, too small to easily lodge in the alveoli (small air sacs at the end of the breathing tubes). It is when viruses are carried by larger particles in the 1 to 5 micrometer range that they tend to stick to the alveoli.
Paper face masks are well suited to catch particles in this size range of 1 to 5 micrometers. Simple paper masks with elastic bands, such as the ones that doctors and nurses wear, are about 99% efficient in catching particles as small as 0.5 micrometers. Particles larger than about 5 micrometers typically get stuck in the breathing tubes before they get to the alveoli and are moved upward and swallowed, or coughed or sneezed out.
Where the action is:
Why is this important? In humans, cells in the upper respiratory tract provide very few receptors to which the present strains of the H5N1 virus can attach, but cells in the lower respiratory tract, especially in the alveoli, provide plenty of opportunities for the virus to do so. (van Riel et al., 2006)[9] Cells down there can’t transport virus-laden particles upward.
It’s the other way around with seasonal influenza viruses. They attach to cells in the upper respiratory tract from which coughs and sneezes can spread the virus around. (Shinya et al., 2006)[10] These findings may also explain why the H5N1 virus can infect humans but does not spread efficiently from person to person.
What to do:
Nobody should expect face masks to provide perfect protection against influenza infection. Touching mouth, nose, or eyes with contaminated fingers is probably a more important route of infection. But together with meticulously washing hands after any touching of potentially infected objects, wearing a face mask is a good first line of defense.
Since there is no discernible harm besides the cost of masks, and looking a bit ridiculous if you are among the first to wear them in public, and since the potential benefit is so great, I find it to be a no-brainer to get hold of a package of masks now and store them in a safe place.
Should a bird flu outbreak occur, I hope I’ll remember where the package is and wear the masks if I have to be around people who may be infected. Hopefully, the bird flu will not turn pandemic, in which case I’ll use the masks when woodworking.
[1] WHO, November 2005.
Clarification: Use of masks by health-care workers in pandemic settings.
http://www.who.int/csr/resources/publications/influenza/Mask%20Clarification10_11.pdf
[6] Severe Acute Respiratory Syndrome (http://www.cdc.gov/ncidod/sars/)
[7] Lau JT, Yang X, Tsui HY, Pang E.
SARS related preventive and risk behaviours practised by Hong Kong-mainland China cross border travellers during the outbreak of the SARS epidemic in Hong Kong.
J Epidemiol Community Health. 2004 Dec;58(12):988-96.
[8] Wu J, Xu F, Zhou W, Feikin DR, Lin CY, He X, Zhu Z, Liang W, Chin DP, Schuchat A.
Risk factors for SARS among persons without known contact with SARS patients, Beijing, China.
Emerg Infect Dis. 2004 Feb;10(2):210-6.
[9] Van Riel D, Munster VJ, de Wit E, Rimmelzwaan GF, Fouchier RA, Osterhaus AD, Kuiken T.
H5N1 virus attachment to lower respiratory tract.
Science, published online 23 Mar 2006; 10.1126/science.1125548.
[10] Shinya K, Ebina M, Yamada S, Ono M, Kasai N, Kawaoka Y.
Avian flu: Influenza virus receptors in the human airway
Nature 23 March 2006;440:435-436; doi:10.1038/440435a
There are several types of masks available, is there a particular type that is the best protection and able to catch the small particles you describe?
Posted by: Richard J. | March 27, 2006 at 03:26 PM
Unable to find any info that would indicate how long an outbreak would last, once discovered.
Posted by: Jo Ann Pisane | April 14, 2006 at 05:35 PM