Ask the Doctors

Dear Doctor: How does the flu virus spread? I've always thought it was mostly from coughing, which contaminates the air and the surfaces we touch. But now I've heard that people who are sick actually breathe the virus out. Should I be wearing a mask to protect myself?

Dear Reader: One of the more challenging points to get across regarding the flu has been just how contagious a sufferer is, and how early into a bout of the illness that contagion begins. Now comes research that makes understanding (and acting on) this information all the more crucial.

You're correct that the assumption has been that it's by coughing that we pump aerosolized droplets of moisture, which contain the flu virus, into the air and onto the surfaces around us. We've known for some time that these droplets can hang in the air for up to several hours and can live on hard surfaces for several days. But the results of a recently published study by scientists at the University of Maryland's School of Public Health show that by simply breathing, a person who is sick with the flu is exhaling the virus.

The researchers examined the mechanics of how 142 university students with confirmed cases of influenza sent the virus into the air around them. The participants in the study sat in front of a device that could measure various sizes of the aerosolized droplets they dispersed while coughing, sneezing, talking or breathing. In 218 sessions that lasted 30 minutes each, it was revealed that close to half of the airborne droplets that contained the flu virus were collected in the absence of coughing. Since the participants rarely sneezed, the takeaway was that people with an active infection are dispersing the virus into the air around them when they breathe.

An earlier study from the University of Hong Kong concluded that half of flu infections within households are passed along via aerosolized droplets. The study also looked into your question of whether wearing a surgical mask would prevent infection. The answer echoes the findings of several similar studies -- basically, no. Though masks may slightly reduce risk by screening out the largest droplets, they are not effective against the fine aerosolized mist from the breath. According to the Centers for Disease Control and Prevention, the people who really should be wearing facial masks are individuals who are ill.

It's important to note that the University of Maryland study did not tackle the specific question of how the flu is transmitted. Still, the findings do suggest that, even in the absence of coughing, people with the flu can send the virus into the environment around them.

All of which leads to advice that physicians have been giving -- and which patients have been ignoring -- for generations. And for emphasis, we're putting it into a paragraph of its own:

Stay home when you're sick.

Not only do you really and truly need to rest in order to give your body the best shot at recovering from influenza, but venturing forth while you're actively ill puts everyone around you at risk.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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