individual's mere presence in a room stirs up 37 million bugs
every hour - actually material left behind on the floor by
previous occupants, says a new study.
"We live in this microbial soup, and a big ingredient is our own
micro-organisms," said Jordan Peccia, associate professor of
environmental engineering at Yale University and the principal
"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," said Peccia, the journal Indoor Air reports.
This is the first study that quantifies how much a lone human
presence affects the level of indoor biological aerosols,
according to a Yale statement.
Peccia and his team measured and analysed biological particles in
a single, groundfloor university classroom over a period of eight
days - four days occupied, and four days vacant.
At all times the windows and doors were kept closed. The heating,
ventilation and air conditioning (HVAC) system was operated upon
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.
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
Of the 15 most abundant varieties of bacteria identified in the
room studied, four are directly linked with humans, including the
most abundant, Propionibacterineae, common on human skin.