Masks' flu protection assessed

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Masks' flu protection assessed

Experts unsure how effective they are against disease

Brown, Washington Post

Friday, April 28, 2006

Washington -- A flu epidemic 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 Thursday.

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 aren't 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

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 the release of

the 97-page report requested by the U.S. Department of Health and

Human Services.

What little is known about masks and respiratory infections comes

from research on tuberculosis and SARS (severe acute respiratory

syndrome), two infections that influenza might not mimic.

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 each.

" 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 made out of spun-plastic fibers, but fit tighter.

They don't work well on people who have beards.

N95 respirators, which cost $1 to $3 each, are designed to filter out

95 percent of particles that measure 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.

Masks and respirators stop particles three ways. Large particles and

droplets can be stopped by their outer surface; smaller particles can

be stopped by the mesh; and even smaller particles can be stuck to

individual mask fibers by electrostatic charge.

In general, surgical masks will be most useful for people already

infected with influenza, preventing them from coughing virus-laden

droplets of saliva and mucus into the environment.

The N95 respirators will be 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 clearly occurs.

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