With You in the Room, Bacteria Counts Spike
“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 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 bacteria that we breathe.”
Many previous studies have surveyed the variety of germs present in everyday spaces. But this is the first study that quantifies how much a lone human presence affects the level of indoor biological aerosols.
Peccia and his research team 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. 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.
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.
The results could also be of use in space exploration. Techniques for improving air quality are useful in providing a safe environment for human explorers in enclosed habitats like the International Space Station. Additionally, understanding how humans introduce microorganisms into an environment can help us develop better techniques for sterilizing equipment for future planetary missions. When a mission like the Mars Science Laboratory is sent to a location like Mars, it is essential that there are no microbial contaminants traveling along for the ride.