Researchers say each person sheds 37 million bacteria per hour each hour spent occupying a room. (Jeremy Wilburn: Flickr)
Researchers say each person sheds 37 million bacteria per hour each hour spent occupying a room. (Jeremy Wilburn: Flickr)

Our colleagues at California Watch have a yuck-inducing story today about indoor air quality. It turns out, Susanne Rust says, “You are a big bag of germs. And just by walking into a room, you add 37 million bacteria to the air for every hour you remain there.”

In a study published recently in Indoor Air, researchers at UC Berkeley and Yale University examined the effect of people on indoor air quality. This is the first time the “bacterial sloughing” of people in a room has been quantified, using DNA-based methods, according to UC Berkeley’s William Nazaroff, co-author of the study.

From the California Watch report:

“We live in this microbial soup, and a big ingredient is our own microorganisms,” said Jordan Peccia, associate professor of environmental engineering at Yale and principal investigator of the study. …

“Mostly, people are re-suspending what’s been deposited before,” he said. “The floor dust turns out to be the major source of the bacteria that we breathe.”

California Watch explains that researchers first analyzed a university classroom that was empty for four days. Over the next four days, the room was occasionally occupied.

The researchers found that the presence of a person correlated with significant spikes in fungi and bacteria circulating in the air. In particular, it was the large-fungal particles and medium-sized bacteria that were most prevalent.

They found that nearly one-fifth of all bacteria and fungi measured in the room came from human sources, as opposed to plants or other sources. And the most predominant bacteria was a common human skin critter called Propionibacteria.

And since KQED’s newsroom has wall to wall carpet–which I am standing on right now–I was not happy to learn the researchers reported that carpeted rooms were the “most infested.” YUCK again. Still, is this really any surprise?

So what’s it all mean? We already know that bugs are spread human-to-human. Curiously, the co-authors disagreed about the health impact.

While Nazaroff reassuringly tells us that “we don’t yet know whether there is any health significance associated with routine bacteria and fungi exposure indoors.”

Peccia was less sanguine. “All those infectious diseases we get, we get indoors,” he told California Watch.

What to do? A quick check of the Centers for Disease Control website reminds us to wash hands frequently. It’s “one of the most important steps we can take to avoid getting sick and spreading germs to others,” the CDC says.


Forget Cigarettes — Just by Walking in a Room, People Add Bacteria to It 4 April,2012Lisa Aliferis

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Lisa Aliferis

Lisa Aliferis is the founding editor of KQED’s State of Health blog. Since 2011, she’s been writing and editing stories for the site. Before taking up blogging, she toiled for many years (more than we can count) producing health stories for television, including Dateline NBC and San Francisco’s CBS affiliate, KPIX-TV. She also wrote up a handy guide to the Affordable Care Act, especially for Californians. Her work has been honored for many awards. Most recently she was a finalist for “Best Topical Reporting” from the Online News Association. You can follow her on Twitter: @laliferis

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