How Does Bacteria Get Into Your House?

You only have yourself to blame.


Bacteria are in your house, on your pillow and in your gut. We need them, and in many ways they make us who we are, but some bacteria aren’t as welcome. So how do they get into your house in the first place?

At Lab Rat, one of the Scientific American blogs, S.E. Gould points to a recent paper on that very subject. The paper, published in PLoS ONE, looked at the sources and origins of bacteria that are suspended in indoor air. The study looked at a university classroom (they had a few laying around) and counted how many of what kind of bacteria were in the room. The researchers then compared those bacterial species the set of bacteria found on human skin, outdoor air and indoor floor dust.

Unsurprisingly, the more people there were in the room, the more particulates there were in the air. So the researchers wanted to see where that was coming from. Gould explains the next step:

To further explore the effect of room occupancy on the effect of indoor particles they compared three situations – one where a single person walked in over the carpet, one where a single person walked in over a plastic sheeting covering the carpet (to prevent re-suspension of floor particles) and one where 30 people walked in over the plastic sheeting. The table below shows that the carpet was the major source for re-suspended large particles in the air, although with enough people large particles were still found floating around (unfortunately the experiment with 30 people was only carried out once, so there are no error bars).

In other words, it’s your carpet and not the people walking on it that coughs bacteria into the air. The study showed that humans are a big factor in how bacteria gets around. We introduce it from our hair and skin, and we kick it up by just being in a space. Clearly the solution to bacteria-free homes is to remove the people.

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