As a microbiologist learning a little bit about building science, I was fascinated to hear early on about how little was actually known about the causative effect of particular microbes on human health in the built environment. I had assumed that we knew a lot about which species of fungi (mold) and bacteria caused problems in the built environment. It turns out that the best two ways of predicting the presence of health problems in a building are visible water damage and a “moldy smell”. These correlations, and the lack of correlation to any particular species of microbe has been supported by a lot of epidemiological work. There’s a wonderful 2011 review on this topic by Mark Mendell from the CA Department of Health for anyone who wants to learn more.
Therefore I was interested to see the following headline this week “Research Identifies Specific Bacteria Linked to Indoor Water-Damage and Mold”. This work, from the University of Cincinnati is part of a large Housing and Urban Development (HUD) project on health hazards in the home. The researchers measured the “cumulative mold burden” of homes via a standard DNA-based measure of 36 mold species called the “environmental relative moldiness index” or ERMI. Then they looked for bacteria as well. They found correlations between Stenotrophomonas and the ERMI, and between Mycobacterium and visible mold on the home.
On the one hand, I think it’s great that people are looking at these correlations and trying to get some sort of handle on what species in the built environment might be important for human health. On the other hand, since there’s no proven correlation between ERMI and any health issues we’re talking about a correlation of bacteria to a possible correlation of mold and health. That’s a lot of steps and all of them are missing causation.