Is the ERMI Test for Mold Accurate?

Written By Brantley May

The Environmental Relative Moldiness Index (ERMI) has been becoming an increasingly popular testing method to check for mold in homes. This test is often recommended by healthcare providers who do not have a background in Environmental Sciences and don’t understand the limitations of this testing method.

However, amongst environmental scientists, the limitations of the ERMI test are well-known, and for that reason, true experts avoid this method.

There isn’t just one thing that makes the ERMI test inaccurate. There are many. Compiled below is a list of reasons why this test should not be used for indoor mold testing. As long as this list is, surprisingly, there are more reasons that are too detailed to cover here.

That being said, below is a list of just some of the reasons why the ERMI should be avoided.


The ERMI was initially designed for use on a single research project.

This research project was created and funded by the Environmental Protection Agency (EPA). The EPA has explicitly been telling the public to stop using this test and that is is not accurate.¹

If the creator of the technology says you should stop using it, that should tell you something.

The project aimed to find correlations between mold in homes and asthma.² The researchers tested around 1,000 homes and came up with an “average moldiness” in homes. It’s very important to realize that the “good” or “bad” ERMI score was completely made up by computer modeling, meaning they never actually went out and verified it with other methods.²

In scientific research, modeling is always a good start, but something must be verified before calling it “true.”

Imagine that I built a house in a computer model and told you that it is a perfect house, and all the simulated water I poured on it runs off perfectly, and it doesn’t leak. Well, that can’t be verified until I actually build that house and test it.

The funny thing is that ERMI researchers know the test isn’t accurate because they never completed the research or had it verified. For this reason, the EPA (who did the research) says that you shouldn’t use this for testing. We could continue to go on about other reasons the research was inaccurate, but it shouldn’t matter with the above information alone.

Imagine if there were blood tests, vaccines, or medicines that had never been verified as safe and effective. Would you take them?


Below is a quote from the head researcher on the ERMI project²:

“As the approach has not been validated through a multi-lab study, we cannot comment on the accuracy of information obtained from others using ERMI. Inspection for water damage and mold remains the key to current EPA mold-assessment guidance.”

-Kevin Oshima, Ph.D.

Center for Environmental Measurement and Modeling

Here is another quote from the team that created the ERMI³:

“There is a risk that the public may make inappropriate decisions regarding indoor mold on the belief that ERMI results were based on research tools fully validated.”


Nobody is performing the test the way the researchers did.

The testing method for the research was performed by vacuuming two square meters of carpet in the living room and every bedroom for five minutes each, with a special vacuum tip. Firstly, does this method sound like it can be quantified and compared from house to house? The method is for “every bedroom.” So the test will obviously show different levels between a house with one bedroom and a house with five, yet they are being directly compared. What about the suction rate of the vacuums? Is that being noted? Do all vacuums pull the same amount of dust? What type of carpet? These things will surely affect the suction rate. There is no specification on where to vacuum, either. In the center of the room where most of the traffic is, or in the corner? There are too many variables that make even the research questionable, and the list goes on. This is not how testing and research should be performed. All data points should be equal.

As noted, the test uses a vacuum with a special tip on two square meters of carpet for five minutes. Does this sound like the method people use in their homes? Not at all. People are now using cloths and Swiffers to grab dust from basically wherever they want with no regard for the volume, weight, surface area, etc. This is not scientifically accurate. You cannot use a cloth for a test designed for a vacuum.

Imagine checking your blood sugar, and the proper way to do it is to prick your finger and let the blood land on a glucose strip. You get an accurate reading.

Now try peeing on a glucose trip instead. Should you expect to get the same result? Heck no! Imagine it tells you that your glucose level is ten times the amount it actually is (or ten times less). People who truly believe this number is accurate would be terrified for their health.

This is exactly what is happening with the ERMI.

Official research has already been performed comparing cloth sampling versus the original vacuum sampling for the ERMI.⁴ The results showed widely different levels between the two—and many other disagreements.⁴ For example, the research showed the average Stachybotrys CE/mg for vacuuming was 1.5, while the Swiffer method showed 10.2! That is nearly seven times more in the same exact environments.⁴ It can’t be trusted.

Below is a table and graph showing the differences in accuracy between doing the ERMI with a Swiffer cloth versus the original method of using a vacuum:

 
 


What do the numbers actually mean?

Let’s assume that the results you received back are accurate (which is a huge assumption). How do we know if they are bad or good? Simply put, we don’t. The results given are just arbitrary numbers that have never been validated. They are made up. Nobody has ever looked at the numbers to see at what point the numbers start getting “unhealthy.” And even if they did, it wouldn’t matter because everyone’s body is different.

Imagine you went to a doctor’s office for a health examination and said you weren’t feeling well. He takes a reading of your heart and says:

👨‍⚕️ “Your heart level is 5”.

🙍‍♀️ “Okay, Doc, is that good or bad?”

👨‍⚕️ “I don’t know; we never did the research. It’s just 5”.

🤦‍♀️ “So it’s literally just a number that doesn’t tell me anything?”

👨‍⚕️ “Yep. That’ll be $500.”

That’s the ERMI.


The ERMI Score doesn’t make sense.

The ERMI uses this convoluted score called the ERMI Score, in which they take the difference between 26 “good” molds and 10 “bad” molds. First of all, what the heck is a “good mold”? That answer cannot be defined in this test because it doesn’t make sense.

One of the main issues is how the formula treats outdoor spores. The formula separates the mold spores that usually grow outdoors from those that are associated with water damage. Unfortunately, this is a difficult distinction to make. Cladosporium, for instance, is one of the most common forms of mold growth found in places with existing indoor moisture problems. Yet, the ERMI formula positions it as an “outdoor mold spore.” Cladosporium is a ubiquitous mold found both indoors and outdoors. Thus, if a home had significant levels of Cladosporium growing indoors, it would simply be subtracted from the data, and the house would achieve a clean bill of health.

So this is an oversimplified version of how the score works. Follow me here:

Let’s say you had 6 bad molds and 8 good molds. Do you know what the ERMI does? It subtracts the good molds from the bad molds. So:

6 - 8 = -2. Your ERMI score is -2. You’re good!

But wait, what about the 6 bad molds?

“Oh, don’t worry about those because you have 8 good molds to cancel them out.”

HUH?

Okay, so let’s pretend that we remediated the house that had the -2 result above.
After thorough remediation, they removed a lot of mold! You ERMI test again (which they can’t be compared easily anyway, but we will get into that later).
You get 3 bad molds and 0 good molds.

3 - 0 = 3. Oh, your ERMI score went UP! It’s worse in here now.

Wait… But most of the mold is gone? It makes no sense.


ERMI doesn’t help quantify mycotoxin risks.

The public mainly uses ERMI to try and discover health effects related to mycotoxins. But remember, the research was designed for connections to asthma. There is a large difference between allergenic and toxic mold effects. The study wasn’t concerned about mycotoxins in the slightest, so it isn’t tailored for that.

Again, the numbers you get from the test are not to tell you how bad the toxins are. It’s never even mentioned in the original research, yet here we are using it for that.

Did you know that many of the molds on the ERMI test don’t actually produce mycotoxins? Yet, they are contributing to the final score.

Imagine going to the doctor, and they check your ears to see if you have strep throat.
This is the ERMI.


The ERMI can’t assess true exposure levels.

ERMI testing doesn’t tell you what is in your breathing space. It can’t be correlated to what type of spores are being inhaled and in what concentration. In other words, it tells you nothing about your actual inhalation exposure risks.

Many spores are wet and sticky and don’t get dispersed in the air easily. Some are larger than others. Some are less aerodynamic. Some travel extremely well, while others need bugs to travel on! The list goes on. ERMI cannot tell us what you’re breathing.

The testing methods are difficult to repeat or compare accurately.

Remember that the ERMI score is completely dependent on comparing your home with the homes tested in the research.² If different ERMI tests can’t be compared to each other accurately, then how accurate is the score?

It is easy to understand the limitations of the ERMI test by comparing it to the air sample test. Air samplers draw air for a specified period at a set air flow rate.

This generates a consistent and repeatable volume of air across the sample media. By measuring exactly the same volume of air in each sample, we are able to compare different samples with a high level of success.

The ERMI test is quite different. The amount of sampling may be highly variable. With the Swiffer-style sampling technique to collect dust, as might be expected, it’s extremely difficult to quantify Swiffer sampling. Therefore, comparing different tests is near impossible.

Imagine going to a doctor and they analyze four liters of blood and give you results based on a four-liter concentration. Now, someone else goes to the doctor and they have ten liters of blood taken, but the doctor is still giving you results based on a four-liter concentration.
Maybe you decide to go back to the doctor after some months to see if you are getting better, and they only take two liters of blood but compare them all as equal and use the same measurements and concentration formulas. This is the ERMI.



ERMI cannot determine current conditions or tell you where the mold is coming from.

The ERMI test uses settled dust as the sample material, which doesn’t necessarily tell us about the current conditions.²
It may be hard to know how much time has passed since the last time the sampled surface was cleaned. Has it been 3 weeks, or maybe 3 months? The difference in time could be significant, which would naturally produce different results.

Let’s say a home hasn’t had any mold problems for the last two months. However, there was a three-day period three months ago when many mold spores were released while the property owner opened a moldy tent within the home to dry it out.

Perhaps the outside air had a high amount of mold spores for a week, and the windows were left open. Clearly, the elevated mold spores were not part of an ongoing mold issue. But they’re still going to show up in the ERMI sample.

So, sure, cleaning the house should still occur. However, many may believe that there is still an issue and spend a generous amount of time and money to track down a problem in their house which may have been caused by some windows being left open three months ago, which would be impossible for any inspector to determine.


Conclusions

The testing method that ERMI uses (PCR testing of dust) has its place in the testing world, but it must be used strategically, and the person performing the tests must know the limitations.

If you choose to perform DNA dust sampling, there are tests other than the ERMI that use a PCR dust method that should be used instead.

Even still, many of the limitations are similar, and the test should be used cautiously. Every testing method (air samples, tape lift, dust, etc.) has limitations. It is important to have a professional come in and do a thorough investigation and allow them to choose the testing method that’s best—as long as it isn’t the ERMI.

 

About The Author

Brantley is a Building Scientist and Council-Certified Indoor Environmental Consultant with a specialty in Mycology and certified by the McCrone Research Institute and the Oshner Medical Center for the examination and identification of fungal spores and pollen via microscopy.

Brantley is certified by the Building Performance Institute as a Building Analyst, Building Envelope Professional, and Infiltration and Duct Leakage Expert. Brantley also holds several certifications related to the identification of Mycotoxins, Water Damage, Odor Control, Structural Drying, Infectious Disease Control, and Energy efficiency issues and is a student of Mechanical Engineering.

He is also a state-licensed mold assessor who carries the credentials for teaching and proctoring exams for other professionals to receive their state accreditations and certifications in mold and environmental-related services.

 
Brantley May
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