ERMI Testing

ERMI: Environmental Relative Mouldiness Index


Performing an ERMI is a way to determine whether the presence of water damage in a building (WDB), has caused mould amplification, which can very likely cause negative health consequences to the occupants.

Samples for ERMI are analysed using Mould Specific Quantitative Polymerase Chain Reaction (MSqPCR). Data obtained from this is assessed and interpreted by reference to a database of similar ERMI data acquired from normal homes. The test is an objective, sensitive and standardised method that can identify and quantify selected mould species.

The usual sample is settled dust collected in homes and buildings to determine the concentrations of the DNA of the different species of mould. While there is a wide spectrum of moulds that can be analysed in this way, 36 species of mould are detected. The research on which the procedure is based selected 26 of those moulds as being associated with WDB (the Group 1 mould) and 10 common species (Group 2) that were not found to be associated with WDB. The first step to calculate the ERMI is to total the individual log10 of the Group 1 mould and then total the individual log10 of the Group 2 moulds. The ERMI is then the difference between these two totals.

Simply put, a home or building with a high ERMI value has a greater chance of causing a mould problem for its occupants than those with a lower ERMI.

ERMI Background

The US Environmental Protection Authority (USEPA) developed ERMI to provide a straightforward, objective, sensitive and standardised way to assess mould using a ranking system based on dust samples collected from homes. The ERMI will help predict the mouldiness of homes.

Based on widely published data from EPA researchers and the 2006 HUD American Healthy Home Survey, the test has been developed as a tool to evaluate the potential risk of indoor mould growth and associated health effects on occupants.

In order to most effectively use this tool, the ERMI obtained needs to be compared to a national database. Indices were determined using this method for 1,096 homes across the U.S. as part of the 2006 HUD American Healthy Home Survey. Individual indices, ranked from lowest to highest were used to create a national Relative Mouldiness Index (RMI) Scale.

In initial studies by the USEPA, the concentrations of different mould species in “mouldy homes” (homes with visible mould growth or a history of water damage) and “reference homes” (homes with no visible mould) were compared. Based on those results, mould species were selected and grouped into those with higher concentrations in mouldy homes (group 1) and those with lower concentrations (group 2). To calculate the ERMI the individual concentrations of the mould species detected are log-transformed and the sum of group 2 logs is subtracted from the sum of group 1 logs.

ERMI = Sum of Log10 Group I minus Sum of Log10 Group II

MSqPCR - DNA Testing

The ERMI process involves the analysis of a sample of dust from a home or other building. Dust is first extracted from the sample provided, then fungal DNA is extracted and purified from the dust. This fungal DNA is then analysed using MSqPCR. This is a highly specific DNA-based method for quantifying mould species.

ERMI Graph

The ERMI graph makes it possible to compare one house’s “mouldiness” with another without being a statistician.

This table assists with interpreting the graph:

Quartile Zone Percentage ERMI Value Relative Mouldiness
25% of houses
Between -10 to -4
Low Relative Mouldiness
25% of houses
Between -4 to 0
Low to Medium
25% of houses
Between 0 to 5
Medium to High
25% of houses
Between 5 to 20
Greater than 20
Very High

Mould Species Identification

One of the reasons why the ERMI has become such a powerful test for mould is that it also provides detailed information relating to the identification of species of mould present. Traditional methods of mould sampling, such as air sampling and microscopic identification, fail to identify moulds to species because some species of mould have virtually identical spore structures often making it impossible to distinguish between them.

Why Species Identification is Important

Determining the species of mould can be helpful for a number of reasons. One of which is that certain moulds are associated with certain substrates. For example, Stachybotrys grows well on wet cellulosic material, so if it is present an assessor will look in the walls as Gyprock/drywall could be that source. Other species of mould are associated with flooring and carpeting so if certain types of mould are present they might indicate a problem behind carpet or other floorings.

From the perspective of the health of occupants, there are published relationships between certain mould species and deleterious health consequences.

Vacuum Sampling

NSJ Enviro offers two methods for collecting dust samples. The original ERMI process used vacuum dust sampling where a special nozzle is fitted to a vacuum cleaner and a sample of dust is taken by masking off a 900 x 1800mm rectangle in the occupant's living room and a similar area in the master bedroom. They are each vacuumed for 5 minutes to obtain a composite sample. One clear advantage of this test is that the carpet acts as a repository for the mould spores to collect over time. An issue that also occurs is that when a home has been water damaged the carpet may have been removed.

Swiffer Cloth Sampling

One clear limitation of ERMI vacuum sampling is that many homes do not have carpet, and many people who are susceptible to mould-related illness have chosen to have wooden or tiled floors. As a result, a sterilised swiffer cloth is used to collect the dust. It is important when sampling to collect enough dust for analysis, at least 5mg.

HERTSMI-2 Testing


HERTSMI-2 is a DNA-based MSqPCR test that analyses the dust sample provided for 5 particular moulds. These moulds are known as the “Big 5”. HERTSMI-2 is an acronym for Health Effects Roster of Type Specific Formers of Mycotoxins and Inflammagens – 2nd Version. The HERTSMI-2 score provides an indicator for people suffering from Chronic Inflammatory Response Syndrome or CIRS, as to whether or not it is safe for them to occupy their home without recurrence of symptoms.

How does HERTSMI-2 Differ from ERMI Testing ?

HERTSMI-2 differs from ERMI Testing in a few ways;

  • HERTSMI-2 Testing looks at 5 moulds while ERMI looks at 36 mould species.
  • The ERMI gives the result as an easy-to-understand comparison to an established database of water-damaged buildings and non-water-damaged buildings.
  • As HERTSMI-2 Analyses for 5 moulds and is cheaper to do the analysis compared to 36 for the ERMI.

Which Mould Species are Identified in HERTSMI-2?

  • Aspergillus Penicilloides
  • Aspergillus Versicolor
  • Chaetomium Globosum
  • Stachybotrys Chartarum
  • Wallemia Sebi

How Can the HERTSMI-2 Score be Used ?

A HERTSMI-2 score <10 is indicative that the building is safe for re-occupancy.


PCR Detection and Confirmation

Polymerase Chain Reaction or PCR technology is used by our lab as a detection method for various organisms using specially designed probes and primers developed exclusively for the laboratory.

Fungal or bacterial DNA is extracted, purified and combined with specific primer-probe mixes to identify the species of mould or bacteria that may be present in the sample.

At NSJ Enviro we can perform presence/absence PCR detection for a number of microbes, including Human Bacteroides and Actinomyces, from a variety of sample types.

Other organisms can be detected by special request. Please contact the lab today for more information.

NextGen Sequencing

Next Generation Sequencing or NGS, involves the massively parallel sequencing of millions of DNA fragments, which minimises the need for fragment cloning used in traditional Sanger sequencing methods. Parallel sequencing provides vast amounts of data quickly and at an affordable cost. This enables in-depth analysis of entire genomes at unprecedented levels, allowing researchers to explore questions/hypotheses that previously would have taken years to answer.

Sequencing is the process of determining the precise order of nucleotides within the genome. It includes various methods or technologies that are used to determine the order of the four nucleotides in the DNA strand. The advent of rapid DNA sequencing methods has greatly accelerated biological and medical research and discovery.

Using NGS, we can study how you interact with the microbial co-inhabitants of your home or work – without being limited by the methodological constraints we have been subjected to in the past. NGS will allow us to determine and quantify the fullest spectrum of the microbiota in your environment.


This technology has a vast array of applications, such as:​

  • diagnosing and understanding complex diseases;
  • whole-genome sequencing;
  • analysis of epigenetic modifications;
  • mitochondrial sequencing;
  • transcriptome sequencing – understanding how altered expression of genetic variants affects an organism; and
  • exome sequencing – mutations in the exome are thought to contain up to 90% of mutations in the human genome, which leads to disease.
  • DNA techniques have been used to identify and isolate genes responsible for certain diseases, and provide the correct copy of the defective gene known as genetic testing. With continued advancements in DNA technology, researchers can better understand the underlying genetic causes of diseases and develop more targeted and effective treatments. As genetic testing becomes more widespread and accessible, it has the potential to revolutionize the field of medicine and improve health outcomes for millions of people worldwide.

Example Targets of Interest

Bacteria Panels:​

  • Actinomycetes & Nocardia
  • Mycobacteria
  • Chlamydia
  • Mycoplasma
  • Custom orders where the customer can define their own panel

Mould Panels:

  • Fusarium
  • Exophalia
  • Exerohelium
  • Scedosporium
  • Sporothrix
  • Trichoderma
  • Trichosporun
  • Custom orders where the customer can define their own panel