Use of protective face coverings will be one of many strategies used to slow or prevent transmission of the flu virus in the event of a pandemic, even though scientific evidence about the effectiveness of inexpensive, disposable medical masks and respirators against influenza is limited. Given predictions that these devices will be in short supply if a pandemic strikes in the near future, the U.S. Department of Health and Human Services asked the Institute of Medicine of the National Academies to investigate the potential for reuse of disposable respirators or masks. A new report from IOM says that there is currently no simple, reliable way to decontaminate these devices that would enable people to safely use them more than once.
It is possible that an individual could reuse an N95 respirator by following a series of steps to protect it from contamination, added the committee that wrote the report. However, because the effectiveness of any face coverings against flu is unclear, wearers should not risk unnecessary exposure, committee members emphasized.
"Respiratory protection through the use of face coverings is only one of many strategies that will be needed to slow or halt a pandemic outbreak of influenza, and people should not engage in activities that would increase their risk of exposure to flu just because they have a mask or respirator," said committee co-chair John C. Bailar, professor emeritus, University of Chicago, Chicago. "Even the best respirator or surgical mask will do little to protect a person who uses it incorrectly, and we know relatively little about how effective these devices will be against flu even when they are used correctly," added co-chair Donald S. Burke, professor of international health and epidemiology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore. "Substantial research must be done to increase our understanding of how flu spreads, develop better masks and respirators, and make it easier to decontaminate them."
Many different kinds of medical masks and respirators are available, but the ones being considered for widespread use in an influenza pandemic are inexpensive, disposable medical masks and N95 filtering facepiece respirators. Medical masks fit loosely over the user's nose and mouth and are primarily meant to be worn by health care providers and patients to help maintain a sterile environment by preventing the spread of contaminants by the wearer -- for example, by limiting the dispersal of sneezes and coughs. N95 respirators are used in both medical and industrial settings to prevent the inhalation of harmful microscopic particles by the user. They are designed to fit snugly around the wearer's mouth and nose. When properly fitted, they are certified by the National Institute for Occupational Safety and Health to protect against 95 percent of an aerosolized test substance, although an improper fit compromises their usefulness. Neither N95 respirators nor other forms of face coverings have been tested for their ability to protect against influenza viruses specifically, the committee stressed.
Disposable masks and respirators do not lend themselves to reuse because they work by trapping harmful particles inside the mesh of fibers of which they are made. This hazardous buildup cannot be cleaned out or disinfected without damaging the fibers or other components of the device such as the straps or nose clip, the committee found. Moreover, the committee could not identify any simple modifications to the manufacturing of the devices that would permit reuse, or any changes that would dispense with the need to test the fit of respirators to ensure a wearer is fully protected.
However, the following steps would allow a person to reuse a disposable N95 respirator if necessary. A protective covering such as a medical mask or a clear plastic face shield should be worn over the respirator to protect it from surface contamination. The respirator should be carefully stored between uses, and the wearer should wash his hands before and after handling it and the device used to shield it. These steps are intended for reuse of a respirator by a single person.
There are also reusable respirators that have replaceable filter cartridges, making them another potential alternative in a pandemic outbreak. However, these more sophisticated respirators are costlier than their simpler, disposable cousins.
The committee noted that health care providers in other countries often use washable cotton medical masks. The committee neither recommended nor discouraged the use of these masks or face coverings improvised from towels, sheets, or other cloth. However, the members emphasized that the effectiveness of such masks and improvised coverings against flu is not known.
Data on mask and respirator use and infection rates during the SARS outbreak offer some useful indications of how well people comply with wearing the devices during a medical crisis and on the devices' protective effects, the report notes. But these data are limited, and the findings are sometimes contradictory. It is not clear to what extent use of face coverings and other protective actions -- including hand washing and social distancing -- affected infection rates.
To help develop more effective materials and devices to protect against flu transmission, researchers need to determine more precisely how flu viruses spread from person to person. It is not known whether they disperse as aerosolized particles released in the breath of infected people, spread on larger droplets projected through coughing and sneezing, or are contracted through physical contact with contaminated people and surfaces. Different types of face coverings offer different levels of protection against various forms of harmful agents; for example, masks are fluid-resistant and generally protect better against contaminants dispersed through coughs and sneezes, while respirators protect better against aerosolized contaminants. Research should be done to test how well masks, respirators, and other new filtering materials specifically protect against the spread of flu viruses. In addition, new methods should be developed to decontaminate masks and respirators without damaging them.
The study was sponsored by the U.S. Department of Health and Human Services. Established in 1970 under the charter of the National Academy of Sciences, the Institute of Medicine provides independent, unbiased, evidence-based advice to policymakers, health professionals, industry, and the public.
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