CDC study reveals face masks ineffective against spread of pandemic flu due to Americans' lack of use


ATLANTA Face masks may not be an effective barrier against the spread of pandemic influenza, the Centers for Disease Control and Prevention revealed in a study posted last week on its Web site.

But it’s not because the masks don’t work, it’s because Americans are not likely to wear them.

During the 2006 and 2007 winter seasons, CDC recruited 286 exposed adults from 143 households who had been exposed to a child with clinical respiratory illness. “We found that adherence to mask use significantly reduced the risk for ILI-associated [influenza-like illness] infection, but less than 50% of participants wore masks most of the time,” the CDC noted. “We concluded that household use of face masks is associated with low adherence and is ineffective for controlling seasonal respiratory disease. However, during a severe pandemic when use of face masks might be greater, pandemic transmission in households could be reduced.”

In fact, only 21% of household contacts in the face mask arm self reported wearing the mask often or always during the follow-up period. Adherence with treatments and preventive measures is well known to vary depending on perception of risk, the CDC noted, and that adherence would be expected to increase during an influenza pandemic. During the height of the SARS epidemic of April and May 2003 in Hong Kong, for example, adherence to infection control measures was high, the agency said — 76% of the population wore a face mask, 65% washed their hands after relevant contact and 78% covered their mouths when sneezing or coughing. In addition, adherence may vary depending on cultural context; Asian cultures are more accepting of mask use.

“Results of our study have global relevance to respiratory disease control planning, especially with regard to home care,” the agency noted. “During an influenza pandemic, supplies of antiviral drugs may be limited, and there will be unavoidable delays in the production of a matched pandemic vaccine. For new or emerging respiratory virus infections, no pharmaceutical interventions may be available. Even with seasonal influenza, widespread oseltamivir [Tamiflu] resistance in influenza virus A (H1N1) strains have recently been reported. Masks may therefore play an important role in reducing transmission.”

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