Here’s something the think about the next time you’re in a crowded bar or party: Scientists have found the average person can add 37 million bacteria to the air every hour — simply by stepping into a room and stirring up material on the floor left behind by previous occupants.
The new study, by Yale University engineers, suggests the indoor air we breathe is teeming with biological agents.
"We live in this microbial soup, and a big ingredient is our own microorganisms," said Jordan Peccia, an environmental engineer at Yale who led the study published 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 bacteria that we breathe."
Prior studies have surveyed the number and variety of germs on common surfaces. But the Yale study is the first to quantify how much a lone human presence affects the level of indoor microbes.
Peccia’s research team measured and analyzed bacterial levels in a single university classroom over a period of eight days. The HVAC system was operated at normal levels. Overall, they found that "human occupancy was associated with substantially increased airborne concentrations" of bacteria and fungi of various sizes. Very few of the microbes — less than 0.1 percent — are infectious, he said.
Researchers found that about 18 percent of all bacteria 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, four are directly associated with humans, including the most abundant (Propionibacterineae) common on human skin.
Peccia said the study findings may help engineers design new ways of improving air quality when necessary.
"All those infectious diseases we get, we get indoors," he said, adding that Americans spend more than 90 percent of their time inside.