When Mould Strikes: Understanding the Risks and Taking Action

Mould Testing Methods 

ERMI/ HERTSMI 

The Environmental Relative Mouldiness Index (ERMI) was developed by the EPA’s Office of Research and Development (ORD) as a research tool to investigate mould contamination in homes. The testing used is a mould-specific quantitative polymerase chain reaction (MSQPCR) method that quantifies 36 moulds and calculates a score of relative mouldiness as compared to the reference homes. The score can range from negative ten (-10) to positive twenty (20). The test is conducted using a vacuum to collect dust before sending the sample for analysis. For homes sans carpet, a Swiffer method is used. 

The HERTSMI is a less expensive option, utilising the same collection and testing methods, but for only 5 of the more common indoor mould species. 

Pros 

• Often described as a “snapshot in history” of water damage in a home. 
• PCR method is very precise, and can detect small mould fragments, often missed with other testing methods (e.g., Stachybotrys) 
• ERMI is frequently referred to as the preferred test for treating mould illness and is utilised frequently by mould-literate clinicians 

Cons 

• The test is not suited for detecting the source of where the mould is coming from, as the dust sampled throughout the house is combined during collection 

• ERMI may miss extensive damage if only one area of the house is contaminated, due to the wide distribution of spores 
• Just because an ERMI test comes back with a low score, this doesn’t necessarily mean the house is clean. You and your practitioner should always evaluate the spore count in addition to the score. 

Spore traps/Air Sample 

Spore traps are the current industry standard for mould testing, utilising a pre-calibrated air-flow rate device that samples the air over a pre-determined amount of time, typically 1-5 minutes. The indoor sample is then compared to air quality samples taken from non-compliant locations or outside. 

Pros 

• Primarily used by professional inspectors, and thought to be more standardised than other methods 
• Often necessary for identifying sources of mould growth 
• Able to detect more species than ERMI/HERTSMI 

Cons 

• Results can be impacted by improper testing methods 

• Only utilised by professionals 
• May miss unseen mould growth if the concentration of spores in the air is low during the collection time. 
• Will only test for viable organisms (i.e., intact mould spores, bacteria, yeast) 

Testing visible mould growth can be done by removing portions of contaminated building, or sampling surfaces with a sterile swab or tape. 

Bulk material and surface tests 

Pros 

• Testing damaged materials can detect far more species than ERMI 
• Able to identify moulds that may not be present in the air 
• Little to no equipment is needed 
• Useful for assessing sources of mould that will need to be removed, repaired, or cleaned 

Cons 

• Bulk material testing is usually biased toward viable organisms 
• Risk of releasing mould spores into the air when removing contaminated material 
• Does not assess airborne exposure 

Gravity plates 

Plates can sample dust and mould spores suspended in the air after being placed in a suspected area for a predetermined amount of time. Plates showing mould growth can be sent for laboratory analysis. 

Pros 

• Cost-effective entry point to creating a testing and remediation plan 
• Diverse uses for testing (e.g., able to test the home, car, furniture, carpeting etc.) 
• Good option to assess long-term remediation success 

Cons 

• Prone to false negatives due to poor air circulation 
• May miss heavier mould species that are often not airborne (e.g., Stachybotrys) 
• Less precise than spore traps in identifying the source 
• Only able to detect viable organisms 

DIY Testing – Best practices 

• Collect as many samples as your budget allows 
• Collect samples from areas that you know, or suspect had water damage 
• Collect samples from areas that you spend the most time in 

• Swab all potential visible mould 
• Note areas with strange smells or that feel weird 

DEFINITIONS 

Viable – agent is alive and can grow in suitable conditions. 

Non-viable – agent is not alive, and as such, will not grow despite favourable conditions. 

Working with an expert 

Mould remediation is an expensive process, and deciding whether to work with a professional or DIY should be taken on a case-by-case basis. While there is no correct answer, there are considerations anyone beginning this process should be aware of. Also, be aware that in many cases homeowners do not remediate effectively and can make themselves sicker in the process. Consulting a professional should always be the first before ever considering a DIY option. 

Mould inspectors – vet who you work with 

Mould inspectors are often either microbiologists or someone with experience in the industry. While there are certifications currently available, the reality is all mould inspectors are not created equal. 

Types of inspectors commonly found: 

Visual inspectors – professionals who assess for signs of water damage and mould growth. This approach is not ideal and will miss unseen mould issues. 

Air inspectors – air testing is the most widely used approach for testing mould, and despite its limitations, is one of the best ways to identify sources of mould growth. 

Home health consultants – the third category is professionals who will utilise several tests to fully evaluate the home. They are well-versed in helping individuals suffering from mould-related illness and go beyond current industry standards. 

Resources to consider 

• Home Health Consultants and Mould Professionals 
• Air Filters – although they will not address mould growth they will improve air quality by reducing the concentration of mould spores