With you in the room, bacteria counts spike

Mar 28, 2012

A person's mere presence in a room can add 37 million bacteria to the air every hour -- material largely left behind by previous occupants and stirred up from the floor -- according to new research by Yale University engineers.

"We live in this microbial soup, and a big ingredient is our own ," said Jordan Peccia, associate professor of environmental engineering at Yale and the principal investigator of a study recently published online in the journal Indoor Air. "Mostly people are re-suspending what's been deposited before. The floor dust turns out to be the major source of the that we breathe."

Many previous studies have surveyed the variety of present in everyday spaces. But this is the first study that quantifies how much a lone human presence affects the level of indoor biological .

Peccia and his research team measured and analyzed in a single, ground-floor university classroom over a period of eight days — four days when the room was periodically occupied, and four days when the room was continuously vacant. At all times the windows and doors were kept closed. The HVAC system was operated at normal levels. Researchers sorted the particles by size.

Overall, they found that "human occupancy was associated with substantially increased airborne concentrations" of bacteria and fungi of various sizes. Occupancy resulted in especially large spikes for larger-sized fungal particles and medium-sized bacterial particles. The size of bacteria- and fungi-bearing particles is important, because size affects the degree to which they are likely to be filtered from the air or linger and recirculate, the researchers note.

"Size is the master variable," Peccia said.

Researchers found that about 18 percent of all bacterial emissions in the room — including both fresh and previously deposited bacteria — came from humans, as opposed to plants and other sources. Of the 15 most abundant varieties of bacteria identified in the room studied, four are directly associated with humans, including the most abundant, Propionibacterineae, common on human skin.

Peccia said carpeted rooms appear to retain especially high amounts of microorganisms, but noted that this does not necessarily mean rugs and carpets should be removed. Extremely few of the microorganisms commonly found indoors — less than 0.1 percent — are infectious, he said.

Still, understanding the content and dynamics of indoor biological aerosols is helpful for devising new ways of improving air quality when necessary, he said.

"All those infectious diseases we get, we get indoors," he said, adding that Americans spend more than 90 percent of their time inside.

The researchers have begun a series of similar studies outside the United States.

Explore further: Ideology prevents wheat growers from converting to more profitable methods, new study shows

More information: The paper's lead author is J. Qian of Yale. Other contributors are D. Hospodsky and N. Yamamoto, both of Yale, and W.W. Nazaroff of the University of California–Berkeley.

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hyongx
not rated yet Mar 28, 2012
This is interesting. I just got a air 'purifier' (filter) for my room. Maybe it is psychological, but it makes me feel better.It would be interesting to know the average size of airborne bacteria and the filter size limits.
kevinrtrs
2.3 / 5 (3) Mar 29, 2012
It should actually be an encouragement to stir up the germs:

The human body contains many more germs than cells - and the germs are there for our protection.

This is one of the reasons why it's beneficial to go out and play in the dirt - so as to increase the number and variety of helpful bugs we carry around. Living in an isolated, artificially ventilated space means that the wrong kind(s) of bugs could multiply and overwhelm the presence of the good ones.

Yes, one might feel better after using the HEPA filtration systems but that could mainly be because of the removal of fungal spores, not the bacteria.
JRDarby
not rated yet Mar 29, 2012
I for one welcome our bacterial, uh, cousins? My body's immune system needs something legitimate to fight to keep it from turning on itself, or worse.
roboferret
not rated yet Mar 29, 2012
In addition to KevinRTS' comment, your filter has probably cut down the number of allergens in your room, they can affect you negatively at even a low level. I suspect you have allergies anyway, which prompted the filter purchase?

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