How to Interpret ERMI or HERTSMI Mold Test Results
The ERMI (Environmental Relative Moldiness Index) test is a dust sampling analysis offered by several labs to evaluate the health of a building. ERMI uses a DNA-based method for identifying 36 different species of mold.
Labs currently offering this test include:
- EMSL Analytical ($195-$454 plus shipping)
- EMLab P&K (call the lab for pricing)
- EnviroBiomics ($240-$435)
- Mycometrics ($290, also available through our momsAWARE Online Store)
A smaller version of this test, the HERTSMI (also called the HERTSMI-2), uses similar technology to identify and quantify five of the more common and toxic species of mold. This test is offered by EnviroBiomics ($130-$277) and Mycometrics ($155, also available through our momsAWARE Online Store).
All four labs offer vacuum canisters to collect the dust samples, while Mycometrics and EnviroBiomics also offer the option of using a Swiffer-type cloth to obtain the settled dust.
ERMI Mold Testing
If you suspect elevated levels of mold in your home, it's important to test your environment before cutting into any drywall or lifting any carpet. If mold is an issue, disturbing the spores can make the situation much worse.
Dust sampling is an effective way to assess the health of your environment, and the ERMI (Environmental Relative Moldiness Index) test is recommended as a place to begin.
Several labs offer this analysis, including EMSL Analytical, EMLab P&K, EnviroBiomics, and Mycometrics. Mycometrics offers the simplest form of ERMI testing, using a Swiffer-type AccuCloth Kit, for a cost of $290. They also offer an affordable HERTSMI test option for $155, also using the AccuCloth collection method. Both Mycometrics cloth tests are available through our momsAWARE Online Store.
Below is an interview regarding dust sampling with the late toxicologist Dr. Jack Thrasher, a leader in the field of indoor air quality.
What is the best way for an individual to test a building for toxic mold?
Take note of visual observations and photos of the water damage and mold growth. (Remember, 50 percent of the mold is hidden, thus visual observations are simply a starting point.)
Use a moisture meter with penetrating electrodes to test wall cavities, ceiling, and all other areas of the home. Draw samples from wall cavities that have elevated water content. (Samples will typically be drawn by a hygienist, who will drill small holes and insert a tube to draw an air sample.)
Why is a dust sample preferable to an air sample when testing your home for mold?
Air sampling is unreliable because the results are too variable. Air sampling only identifies mold spores to the genus level. It is important to know the species of mold. Mold spores are present in the dust, and the dust can be examined for species of mold using PCR (ERMI) testing. For example, we tested a building in Bermuda. Initial air samples indicated low concentrations of mold spores. We then disturbed the indoor air with an aerosol of sterile fluoroethane. The spore counts went up as high as 250,000 spores per cubic meter. Thus the spores entrained in dust were redistributed into the indoor air.
Do you recommend the ERMI test as a place to begin when testing for toxic mold?
Yes. The moldiness index is not too meaningful, particularly for sensitive and high-risk people. The portion of the ERMI test that is important is the identification of mold species. Often dangerous molds, such as Aspergillus versicolor, fumigatus, and flavus along with certain species of Penicillium are present. These species cannot be determined by spore counts because Aspergillus and Penicillium species have almost identical spore structures. Also, Stachybotrys does not readily shed spores, but can be found in dust and bulk samples by PCR analysis.
When vacuuming (or using a Swiffer-type cloth) for an ERMI test, is it best to draw dust from one spot, or take from a variety of places around the home?
I personally recommend doing dust samples from various areas of the house. Excellent samples areas are refrigerator coils and other hidden dust accumulation areas (e.g. under washing machines), giving the history of the home since installation of the appliances. Dust from the top of drop-down kitchen cabinets is another source. One can also use carpet dust, although this may not tell the whole story. In conclusion, collect dust from areas in the house that do not readily get cleaned. Keep all dust samples separate from each other—if the dust samples are mixed, one does not know which areas are most contaminated. However, if there is no concern for identifying the areas involved, one can mix the dust samples. I also recommend taking bulk samples of mold growth and subjecting them to an ERMI test.
One may also use a sterile wound-covering gauze to wipe the valleys of the HVAC ducts and gather dust as noted above. Wear sterile rubber gloves and put in a Ziploc bag. Same with the refrigerator. Always do ERMI-36 and mycotoxin testing.*
Is it best to keep the house closed up for a day or two before taking an ERMI sample?
This is not a necessary requirement. The reason is that certain molds are associated with different substrates. For example, Stachybotrys requires a cellulose source, such as drywall, while other species of mold will be associated with flooring and carpeting.
Do I need to vacuum areas that I don't suspect have been affected by the mold?
If mold is indoors and in wall cavities, all areas of the home are probably affected. Therefore do the dust sampling as discussed above. Some areas may have fewer spores than others; however, the mold spores will drift throughout the house.
What about bacteria?
Both Gram-negative and -positive bacteria are also found indoors. The Gram-negative are producers of endotoxins. The Gram-positive release toxins. The Gram-positive bacteria are Staphylococcus, Streptococcus, and various species of Bacillus that can be pathogenic. In addition, the Gram-positive bacteria includes the Actinobacteria, including species of Streptomyces, nontuberculin Mycobacterium, and Nocardia, to name a few. The Actinobacteria are potential pathogens and release toxins into the indoor environment that are more toxic than the mycotoxins produced by molds.
What is involved with taking bulk samples?
Bulk samples are just what the word means. One cuts out a piece of the contaminated materials, e.g. drywall, carpeting, etc. Put it in a Ziploc bag, date and label the bag, and send it to the testing lab. If litigation is involved, then a chain of custody is needed and a witness to the sampling.
If I see visible mold but have no ill health effects, should I still test my home in this way?
Yes. How does one know that they do not have ill health effects? The health effects can range from just sneezing through systemic conditions of not feeling well.
What else is important to emphasize about testing for toxic mold?
Too much emphasis is being put on molds. The indoor environment is a complex mixture of biocontaminants (mold, bacteria, and their by-products).
* Dr. Thrasher recommended mycotoxin dust sampling and urine sampling. Both are available through RealTime Labs.
For more information on Dr. Thrasher's work, visit his website. To learn more about toxic mold, check out Andrea Fabry's helpful resource, Is Your House Making You Sick? A Beginner's Guide to Toxic Mold.