ERMI stands for Environmental Relative Moldiness Index and was created by the U.S. Environmental Protection Agency, Office of Research and Development. The idea behind the ERMI is that dust build-up from around the home (such as on top of the fridge or on the AC filter) is a reservoir for mold and represents mold levels over time. A highly specific DNA-based method for quantifying mold species called mold-specific quantitative polymerase chain reaction (MSQPCR) is conducted on the collected dust to identify 36 different species of mold. The HERTSMI-2 is another test very similar to the ERMI but it’s cheaper and only tests for the five molds most likely to cause health issues.
A few algorithms and calculations later you end up with an “ERMI index” from -10 to 20 which is basically a score for your home as compared to other homes around the nation. Homes with water and mold issues as well as homes with no visible mold are included in this database. There are a lot of variables but an ERMI score of three or more can be too much for mold sensitive individuals. For the HERTSMI-2, the scale is as follows: less than 11 is safe, 11 to 15 is borderline and above 15 is dangerous.
So, what are the advantages of an ERMI or HERTSMI-2? For one, the MSQPCR technology is extremely precise and people like the idea that a single test can determine mold issues in a home or building. The EPA continues to develop the testing and it should become even more useful over time.
On the other hand, I have heard from people who don’t think it’s useful at all and in fact, feel it’s misleading. Some environmental consultants report finding little to no correlation between the ERMI results and the actual material found on site. Another drawback is the cost (several hundred dollars). The sample collection methodology is inconsistent and poorly defined, making accuracy an issue.
The Environmental Mold and Mycotoxin Assessment (EMMA) from RealTime Labs tests for 10 different molds and 16 mycotoxins. They also have a cheaper one that only tests for the mycotoxins. The selling point here, obviously, is that you get info on the mycotoxins and not just the molds. The mold detection technology is called “sensitive molecular detection” and the mycotoxins are identified by what is only described as their “patented Mycotoxin detection test.” Like the ERMI, the EMMA uses dust collected from one or more AC filters. Because it’s newer and designed by a private company (RealTime Labs), there is less info available on the EMMA than on the ERMI.
The Toolman’s Two Cents: I believe all of these tests can be useful and I will continue to make them available to my clients. None of them should be considered a single source of truth. They should represent one data point. One environmental consultant I know drew an analogy to a store-bought pregnancy test. That initial pregnancy test indicates that you need to go see a doctor, get more testing done to confirm there’s a bun in the oven and from there start the process of working with medical professionals to safely navigate the pregnancy. Same thing here. An ERMI or EMMA can be a good first indicator that you have an issue. However, it should be followed up with a thorough inspection by a licensed mold assessor who may or may not recommend additional tests.