ERMI Basics

Updated on January 20, 2016

It’s come to my attention that the previous article Mold Testing may have been a bit too involved. I just wanted to make sure I covered the topic thoroughly. For those that aren’t interested in all the details, I thought it might be useful if I try to strip down what I covered to the basics in this article.

What Is ERMI?

ERMI Vacuum & Cannister

ERMI is a test that looks for the DNA of 36 molds from either a sample taken by vacuuming carpeting or by using a dust cloth. The vacuum sample is captured by attaching a small plastic tube with a filter inside to the end of a standard vacuum hose. The dust sample is captured by using a sterile cloth called a Swiffer Cloth that is swiped over surfaces. The plastic cartridge and Swiffer cloth are sent to a lab that does a mold DNA analysis and sends back an ERMI report.

The ERMI report lists 36 molds that have been divided into two groups, Group I and Group II. There are 26 molds in Group I and these are the molds typically found indoors especially in buildings that have water damage. There are 10 molds in Group II and these are the molds typically found outdoors. In addition to listing the counts for each of the 36 molds, the report also gives an overall ERMI score which is the difference of Group I molds minus Group II molds.


It may seem odd that I’m now going to take a minute to talk about fractions but in the next sections you’ll see why this is important. A fraction consists of the top number (numerator) over, or divided by, the bottom number (denominator). Fraction = numerator/denominator. If you look at the following examples, you’ll realize two truths about fractions. One is that the bigger the numerator, the bigger the overall value of the fraction. The second truth is that the bigger the denominator, the smaller the overall value of the fraction.

15/5=3; 25/5=5; The bigger the numerator (top), the bigger the overall value of the fraction
12/2=6; 12/3=4; The bigger the denominator (bottom), the smaller the overall value of the fraction

Spore E./mg

So now let’s take a closer look at the ERMI report. If you look at the top of the column listing the values for each of the 36 molds, you’ll see it is labeled “Spore E./mg”. It’s a fraction. The numerator (top) is Spore Equivalents and the denominator (bottom) is milligrams of dirt.

ERMI Sample Report

Looking at the numerator (top) first, remember that this is a DNA analysis. This test is very accurate. In other words, every little scrap of mold in the form of spores, chunks of the mold hyphae (fibers), and the like are all measured and counted. Now there’s no way to figure out what part of the total DNA found is from each of the parts of mold. So what they did was to figure out how much DNA you’d get from the average spore of each particular mold and then converted the total DNA found into an equivalent number of spores of that mold – Spore Equivalents.

The denominator (bottom) of this fraction is the milligrams of dirt. Typically what happens is that they sieve out 5 milligrams of the total amount of dirt that is sent in and do a DNA analysis of that 5mg. Once they get the spore equivalents for each of the 36 molds, they divide by 5 to get the number of Spore Equivalents in each milligram of dirt. If you happen to send in less than 5 milligrams, that’s OK too. Let’s say you only send in 3 milligrams. They just divide by 3 instead to come up with the same ratio of Spore Equivalents for each milligram of dirt.

So here comes the key point to this whole article on ERMI. Ready? The key point is that it’s essential to realize that ERMI is really a list of 36 molds showing the number of Spore Equivalents of mold found in relation to each milligram of dirt in the sample sent to the lab. In other words, the 36 values you see listed on an ERMI report are telling you the amount of each mold that was deposited in comparison to the amount of dirt that was deposited. It’s critical to realize that the amount of non-mold (dirt) in the sample influences the values listed on the report just as much as the amount of mold found. I call this the “dirt factor”.


So simply having counts for 36 molds found in each milligram of dirt regardless of the fact that they’ve been very accurately measured is meaningless without some way of knowing at what point the counts become too high – at what point people with CIRS and others get sick. Thankfully, Dr. Shoemaker has very kindly come up with the HERTSMI-2 scoring system. In this system, you simply assign a number to five of the 36 molds listed in ERMI and add them up to come up with your total HERTSMI-2 score. If your score is too high and you have CIRS, the building is not safe. Dr. Shoemaker developed this scoring system based upon thousands of ERMI scores from his patients. By looking at their scores and cross-referencing them against symptoms, he was able to determine that five molds in particular were of most importance and figured out at what levels they made people sick – very cool.

Is Your Home Average?

So let’s look at an example to see how this all plays out. Remember, the ERMI scores Dr. Shoemaker used represent an average of his patient’s ERMI scores. As a result, the more “average” your home is, the more “accurate” the ERMI values in the report will be.

Roughly speaking, the average age of a home in the U.S. is 35 years, with a little over three occupants, and 50% have either a cat or a dog. Based upon my own experience, the carpeting is probably 10 years old, gets cleaned once a year, and although occupants do take off their shoes, they aren’t fanatical about it. You know, average.

So what if you’re a clean freak? Well, mold spores and fragments are everywhere. They’re so tiny, every time you open a window or walk through the door; they enter the building, drift about, and eventually settle to the floor or surface of some sort. That influx is more or less constant and inevitable.

Now let’s say there are two homes next door to each other. Both homes are identical track homes built at the same time and with the same materials. Neither home has an indoor mold problem. Let’s say that in the first house, a very neat retired woman lives. She never wears her shoes indoors. She replaces her carpeting every 5 years.

In the second house, let’s say there is a couple with three kids, a dog, and a cat. The kids are supposed to keep up with chores but the bottom line is it’s hard to keep the house clean. They can’t afford to replace the carpeting.

How will the ERMI scores compare? Remember, ERMI values for each of the molds are given in the number of Spore Equivalent for every milligram of dirt. If the amount of dirt being deposited is greater than average (the denominator is bigger), the each of the mold counts on the ERMI report will be smaller than what it should be. Likewise, if the amount of dirt being deposited is less than average (the denominator is smaller) the mold counts will be skewed higher.

So both homes do an ERMI. Not surprisingly, the home with the single woman comes back very high. The neighbor’s home comes back a little below average. Happily, the woman knows that ERMI results can sometimes be off and calls in a mold expert. The expert knows its important not to simply dismiss a high ERMI score even though he suspects the very clean home and newer carpeting skewed the results. Two side-by-side Swiffer Cloth samples are taken as I’ve described in the article Mold Testing, and the house is shown to be fine.

Does It Matter?

I can tell you from my own experience it matters a lot. My super clean home had an ERMI of roughly 23 and yet when I had inflammatory markers measured according to Dr. Shoemakers’ SAIIE protocol, I was not reacting to living in the house. This was at a time that I was not taking any binders or treatments. I’ve also inspected a dirty home that was an incredible toxic soup with roughly 12 feet by 12 feet of mold growth that had an ERMI less than zero – a very good score. So ERMI values can definitely be way off. If the overall ERMI score is off, then HERTSMI-2 mold counts are off.

Don’t just take my word for it. Talk to experienced mold inspectors – the ones that really care and understand the limitations of mold testing. They’ll tell you flat out that it’s quite common for ERMI to be significantly off. So yes, this does matter.

Is ERMI Useless?

So the temptation may be to simply dismiss ERMI and throw us all back to square zero where we’re left confused and disheartened. That’s not the point of these articles! ERMI is awesome; you just have to know how to use it well.

Furthermore, Dr. Shoemaker’s data doesn’t lie. I have no doubt that a very thorough statistical analysis was done showing the relationship between ERMI spore counts and adverse health effects. Also, ERMI DNA analysis is stunningly accurate. With 99.7% accuracy, they can tell you exactly how many spore equivalents that they found for each of the 36 molds in every milligram of dirt sample you sent in. This is not a test to just throw up your hands and say it’s junk!

Swiffer Cloth

Swiffer Cloth

What about the Swiffer Cloth? The Swiffer Cloth method was not around when Dr. Shoemaker developed the HERTSMI-2 scoring system. As such, HERTSMI-2 was developed using carpet samples only. Almost certainly, the amount of dirt being deposited on top of cabinets and furniture is much less than the amount of dirt being trapped in carpeting. As such, I would anticipate Swiffer Cloth samples to be all skewed high – the denominator (mg of dirt) number is less for Swiffer samples while the numerator (Spore Equivalents) being deposited on both carpeting and furniture is the same.

I was a SurvivingMold Member and wrote in regarding this issue. I was told that when Swiffer samples were compared with vacuum samples, the ERMI scores were essentially the same provided that people did not “scrub” the horizontal surface with the Swiffer Cloth. This is a real conundrum. How can the amount of dirt being deposited on surfaces high up possibly be the same as on the carpeting?

Update January 20, 2016 Note that in the Surviving Mold Swiffer Cloth Method, they no longer say that is important to wipe in one direction. In fact, according to mold remediation expert, Greg Weatherman, it’s best to wipe the area in various directions so as to pick up as much dust as possible. In fact, Swiffer clothes are designed to use electrostatic charge to collect dust. Using gentle back-and-forth motion in multiple directions helps this – don’t scrub the surface. Watch Mr. Weatherman’s video on How to Take an ERMI Sample for more information.

The most likely explanation is that most homes that are water-damaged have a significant mold load. As such, regardless of whether the sample came from carpeting or dusting, the overall HERTSMI-2 score would indicate the building is unsafe – even though the dust samples no doubt tend to be higher. However, in some borderline cases, I would expect that some Swiffer reports may incorrectly indicate the home is unsafe when it isn’t. Said another way, if a Swiffer HERSTMI-2 score comes back OK, then a carpet HERTSMI-2 score would almost certainly be OK too – the building is almost certainly OK.

The Bottom Line

Petri Dish Outdoor Molds Closeup 1

So if you’ve had an ERMI DNA test done and your home is more-or-less average, then chances are very good that the test is accurate and the HERTSMI-2 score you calculate is meaningful. However, if you get an ERMI (or the less expensive HERTSMI) test done and it comes back OK even though you’re having all sorts of difficulty getting better in spite of following protocols, then take a step back and re-examine your ERMI.

Likewise, if you get a super high ERMI, then consider facts like if you took the vacuum sample from new carpeting. If you did, then the Group II molds will be much smaller because they haven’t had the requisite years that it takes to build up to average levels. Remember that the overall ERMI score is calculated by taking the total of all the molds found indoors and subtracting off the total of all the molds found outdoors. Since you don’t have a lot of outdoor molds built up in your new carpeting, your overall ERMI will be way high. Note: You should be very cautious about dismissing high ERMI scores!

The bottom line is ERMI and the HERTSMI-2 scoring systems are awesome; you just have to be a little careful. I hear folks site their HERTSMI-2 scores as if they were “written in stone” and this simply is not the case. If you want a much more accurate way of knowing if a building is moldy, you can take two side-by-side Swiffer Cloth samples and compare them as I’ve outline in the in-depth Mold Testing article I wrote.

By using this improved method, you eliminate the “dirt factor” all together. In this method, you are simply comparing the amount of mold deposited over a given period of time inside the building relative to the amount being deposited outside the building. Although this method is more expensive and takes more time, it is much less prone to error.

I care about you all. I worry that the reason some folks with CIRS aren’t getting better is because they’re in a moldy home even though their HERSTMI-2 came back fine. Similarly, I’d hate to have someone leave their home and belongings without having really tested for mold properly. I’m trying to help. I’m not trying to scare people into thinking the ERMIs they had done are all bad. Most are just fine. However, there will be a few for which this information may prove very useful.