Humans Add Millions of Microbes to the Air Every Hour

Maybe you are sitting alone in your office as you read this.  That is, you think you're alone. You're not. About 37 million friends are joining you every hour.

That's the conclusion of new research from Yale University focused on determining how much bacteria we add to a room simply by being in it. Turns out, the number is hard to fathom.

"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 the principal investigator of a study. "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."

The researchers measured and analyzed biological particles 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 and the HVAC system was operated at normal levels. Researchers sorted the particles by size -- what they describe as "the master variable" because size affects the degree to which particles are likely to be filtered from the air or linger and recirculate.

They found that "human occupancy was associated with substantially increased airborne concentrations" of bacteria and fungi of various sizes. Occupancy resulted in particularly large spikes for bigger fungal particles and medium-sized bacterial particles.

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.

Fortunately for us, only 0.1% of the bacteria is infectious to humans. But since we spend most of our time indoors, that smidgen of infection-inducing organisms has full access to our bodies (just in case you needed another reason to spend more time outdoors).

The study was published in the online journal, Indoor Air.

Posted on May 17, 2012 .