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Surgical Masks Shown to Cut Flu Transmission

Influenza ultrastructure illustration (Dan Higgins, CDC)

Influenza ultrastructure illustration (Dan Higgins, CDC)

Public health researchers at University of Maryland, with colleagues at Harvard, Boston University, and University of Hong Kong identified the main ways flu virus spreads through populations and specifically recommend flu sufferers wear surgical masks to stop the virus. The team led by Maryland and Harvard professor Donald Milton published their findings yesterday in the journal PLoS Pathogens.

Milton and colleagues collected samples of exhaled breath from 37 volunteers who contracted the flu virus within the previous five days. The researchers tested both coarse (5 micrometers or more) and fine (less than 5 micrometers) droplet particles in the exhaled breath for the number of viruses. The results also showed the amount of virus put in the air by flu sufferers varied considerably, from almost undetectable quantitites to 100,000 viruses.

The team found fine airborne particles had 8.8 times more virus than coarse particles. In addition, the fine airborne particles had the highest concentrations of viral RNA copies, making them more infectious. “This has important implications for how we prevent the spread of flu,” says Milton.

The researchers found a few main routes for transmitting the flu virus: direct or indirect contacts with infected people such as doorknobs or keyboards, direct contact with coughs or sneezes that emit the coarse droplets, and direct contact with regular breathing or coughing by a flu sufferer emitting fine airborne particles.

In their data collection, Milton and colleagues took two samples, one with the subject wearing a surgical mask and one without a mask. The Centers for Disease Control and Prevention recommends that people with influenza in health care settings wear surgical masks to prevent transmission of the virus to others. The team found wearing a surgical mask decreases the presence of virus in airborne droplets from exhaled breath. The amount of virus overall was 3.4 times less in when wearing a mask, and 2.8 times less in fine exhaled droplets.

The authors note, “These results suggest an important role for aerosols in transmission of influenza virus and that surgical facemasks worn by infected persons are potentially an effective means of limiting the spread of influenza.”

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