By David Brown
Washington Post Staff Writer
Friday, April 28, 2006
A flu pandemic conjures up images of streets and buses full of people going about their business with masks covering the lower half of their faces. But how useful would those devices actually be?
A 12-person panel of experts, convened by the government, answered part of that question yesterday.
It said that form-fitting molded "respirators" would be better than clothlike surgical masks, and surgical masks would be better than handkerchiefs and scarves. But how much protection any would provide is largely unknown -- as is the question whether they could be safely washed and reused if there were not enough new ones in a pandemic.
"I would not recommend face masks alone. I would not recommend that anyone using a mask think that is adequate protection," said John C. Bailar, a physician and epidemiologist who chaired the committee at the Institute of Medicine that examined the question.
Masks are "part of a package that includes vaccination if it is available, isolation of patients and quarantining, closing of public meetings and schools, 'social distancing' and the washing of hands," he said in a telephone conference with reporters after release of the 97-page report requested by the U.S. Department of Health and Human Services.
Another member of the committee went further in warning people against relying on masks, whose effectiveness in protecting against flu is virtually unstudied.
"Mask and respirator use is considered to be the very last in a series of activities that may be more effective in reducing the spread of flu," said E. John Gallagher, chairman of emergency medicine at Albert Einstein College of Medicine in New York.
What little is known about masks and respiratory infections comes from research on tuberculosis and severe acute respiratory syndrome (SARS), two infections that influenza may not mimic.
Many companies are now stockpiling masks and gloves. The current growth of consumer demand is unknown, however. The Centers for Disease Control and Prevention has about 1 million masks in a national stockpile, with orders placed for 99 million more. Their delivery date, however, is also unknown.
3M and Kimberly-Clark Corp. are the two largest U.S. producers of medical masks. 3M's plants "have been working 24-7 for some time now," said Jacqueline Berry, a company spokeswoman.
Demand for masks in Asia began to rise in January 2005 and in Europe last summer. Since the start of this year, U.S. customers have been ordering more masks, Berry said. She declined to give estimates of 3M's production capacity or say whether orders were backlogged. A spokeswoman for Kimberly-Clark was not able to provide information on its mask production.
Among the many murky aspects of the subject are the names of the devices. "Surgical masks" or "medical masks" are pleated, soft, clothlike objects that cover the nose and mouth and tie behind the head. They cost about 15 cents apiece.
"N95 filtering facepiece respirators" are fitted to the face by molding a cuplike mask that covers the nose and mouth. Like surgical masks, they are also made out of spun plastic fibers, but fit much more tightly. They do not work well with beards.
N95 respirators, which cost $1 to $3 apiece, are designed to filter out 95 percent of particles that measure about 0.3 micrometers, or thousandths of a meter, in diameter. Influenza viruses range in size from 0.08 to 0.12 micrometers, though they are often clumped together or stuck to other airborne debris.
Bulkier rubber respirators with replaceable filters, priced at $25 and up, are used in some non-health-care settings. They were not evaluated by the committee.
Masks and respirators stop particles three ways. Large particles and droplets can be stopped by the outer surface; smaller particles can be stopped by the mesh; and even smaller particles can be stuck to mask fibers by electrostatic charge.
During an epidemic, surgical masks would be most useful for preventing infected people from coughing virus-laden droplets of saliva and mucus into the environment.
The N95 respirators are the most useful in preventing healthy people from becoming infected by "respiratory aerosols" -- microscopic clumps of material left floating in the air when the water in very small droplets evaporates. How often flu is transmitted by aerosols is unknown, but it does occur.
A study found that in a commercial airplane carrying a person ill with a new strain of seasonal flu in 1979, 72 percent of passengers came down with flu. However, the circumstances were unusual; people were kept on the plane for three hours while a broken ventilation system was repaired.
The Institute of Medicine committee said there were no data suggesting that surgical masks or N95 respirators could be cleaned and reused, and advised against doing so.
In a shortage, however, a person could get more time out of a N95 device by wearing it covered with a surgical mask, the panel found. The surgical mask would be thrown away after a day's use, and the respirator stored in a clean bag for use later. This strategy was used in Asia during the SARS outbreak of 2003.