Dry Air Might Boost Flu Transmission

Germs prefer an environment that’s cool, dry and UV-free.

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“Humidifiers may be an important tool to reduce the survival of influenza virus in the home,” authors conclude in the new Environmental Health paper.

Not so fast, says Peter Palese of the Mount Sinai Medical Center in New York City. Knocking out even a significant share of viruses in the air—like one-third—might leave enough behind to cause sickness. And if people aren’t careful, he warns, over-humidifying a building might create a new problem: mold growth.

But Shaman, an atmospheric scientist who studies the effects of moisture and temperature on infectious disease, believes it’s possible that knocking out just 30 percent of airborne flu particles might prove useful.

For a flu outbreak to sustain itself, each infected person must, on average, sicken more than one additional person. Typically, the number averages around 1.4 additional infections. But it’s possible that cutting the number of infectious virus particles indoors by 20 or 30 percent might reduce the average number of people sickened by a flu victim to less than one. “And then,” Shaman says, the outbreak “may die out.”

“It comes down to a numbers game,” he says. It also points to the importance of follow-up field tests to quantify the extent to which relatively modest changes in virus particles’ infectious lifespan may affect the transmission of disease.

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