ERMI Testing

ERMI: Environmental Relative Mouldiness Index



Performing an ERMI is a way to determine if the environment in a home or other building, which has been subject to water intrusion (WDB), has suffered from mould amplification likely to cause deleterious health consequences to occupants.

Samples for ERMI are analysed using Mould Specific Polymerase Chain Reaction (MSQPCR) methods. Data obtained from this is assessed and interpreted by reference to a database of similar ERMI data acquired 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 moulds) 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 moulds 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 lower ERMI.


ERMI Background

The US Environmental Protection Authority developed ERMI to provide a straightforward, objective, sensitive and standardised way to assess mould and indoor air quality investigations. The USEPA developed the ERMI as 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 to 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

As stated ERMI process involves the analysis of a sample of dust from a home or other building. The sample is first analysed using mould-specific quantitative polymerase chain reaction (MSQPCR). This is a highly specific DNA-based method for quantifying mould species. After extraction of the dust, the fungal DNA in the extract is then detected by using specific probes and primers in a qPCR instrument.

MouldLab are currently establishing this methodology and validating it in the Australian setting in collaboration with an associated laboratory. The evaluation of the Australian analyses will be referenced to the Australian Environmental Relative Mould Index (AERMI).

If you are a researcher in Australia looking to conduct research on Australian water damaged buildings and health effects we would be keen to discuss opportunities for research collaboration.


ERMI Graph


The ERMI graph makes it possible to compare one houses "mouldiness" with another without being a statistician. .

This table assists with interpreting the graph

Quartile Zone Percentage ERMI Value Relative Mouldiness
Q1 Green 25% of houses Between -10 to -4 Low Relative Mouldiness
Q2 Amber 25% of houses Between -4 to 0 Low to Medium
Q3 Amber 25% of houses Between 0 to 5 Medium to High
Q4 Red 25% of houses Between 5 to 20 High
  Red   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 those using 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 identify them by these methods. 

Why Species Identification is Important

Using an ERMI to determine the species of mould can be helpful in a mould investigation for a number of reasons. One of the reasons is that certain moulds are associaated with different substrates. For example Stachybotrys grows well on wet cellulasic 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 flooring. 

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

Vacuum Sampling

MouldLab offer 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 allowed a sample of dust to be taken by masking off a 900 x 1800mm rectangle in the occupants 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. We have included a video on the product page that outlines the steps for vacuum sampling.

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, the "Swiffer Cloth Method" was developed. The important issue when sampling is that the procedure needs to collect dust that is representative of the area sampled, providing sufficient quantity of dust so that the lab analysis can be successful.