The most common question I get from people who already know a little bit about mold testing is some version of: "Should I do ERMI or HERTSMI-2 or Pathways™, or all three?" The honest answer is “it depends on what question you are trying to answer,” but that answer is useless without the underlying decision framework. Here is the framework.

Each of the four major investigative tools in modern mold assessment, ERMI, HERTSMI-2, Pathways™, and conventional spore-trap air sampling, measures a different thing. Picking the right one is mostly a matter of matching the test to the question. Picking the wrong one wastes money and, worse, produces a number that doesn’t answer the question you actually had.

ERMI: the 36-species DNA dust analysis

ERMI stands for Environmental Relative Moldiness Index. It was developed at the U.S. Environmental Protection Agency’s Cincinnati lab in the mid-2000s and is based on the analysis of settled dust using quantitative polymerase chain reaction (qPCR) for 36 specific mold species. Twenty-six of those species are associated with water-damaged indoor environments (the “Group 1” species), and ten are commonly found in normal outdoor environments (the “Group 2” species).

The score is a single number, calculated as the log-sum of Group 1 species spore equivalents minus the log-sum of Group 2 species spore equivalents. EPA’s original calibration used dust samples from approximately 1,100 U.S. homes in the HUD American Healthy Homes Survey to produce a national reference distribution. A house in the top quartile of ERMI scores (roughly 5.0 and above) is considered to have a substantial water-damage species load relative to the national average.

What ERMI tells you well: a comprehensive snapshot of the cumulative DNA-detectable species composition of the dust in a building. It is essentially asking “over the last several months to years, what species have shed enough DNA into the settled dust of this home to be detected?” It is very good at identifying historical or hidden water damage that has produced enough biological material to leave a fingerprint in the dust.

What ERMI does not tell you well: current airborne exposure (settled dust is not what you breathe in real-time), the exact location of a source (it’s a whole-building average), or whether the indicator species are actively growing now or were active years ago.

Sample collection: a Swiffer-style dust sample collected by the inspector or, in some workflows, the homeowner under a written protocol. Typical Florida turnaround is 7 to 10 business days from the EPA-licensee laboratory.

Cost range in Florida: roughly $325 to $475 inclusive of sample collection and report interpretation.

HERTSMI-2: the focused 5-species subset

HERTSMI-2 stands for Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens, Second Version. It is a focused subset of ERMI, restricted to five species that Dr. Ritchie Shoemaker identified as the most clinically relevant for patients being evaluated for Chronic Inflammatory Response Syndrome (CIRS). Those five species are Aspergillus penicillioides, Aspergillus versicolor, Chaetomium globosum, Stachybotrys chartarum, and Wallemia sebi.

The HERTSMI-2 score is calculated from the spore-equivalent counts of those five species using a published scoring rubric. The Shoemaker re-occupancy threshold, widely used in the CIRS clinical community, is a score of 10 or less for a building considered safe for a CIRS patient to occupy. Scores between 11 and 15 are borderline. Scores above 15 are not recommended for re-occupancy by a sensitized patient.

What HERTSMI-2 tells you well: whether the five most clinically problematic indoor mold species are present at concentrations that have been correlated with patient symptom flares in the Shoemaker patient cohort. It is the standard tool for a CIRS clinician deciding whether a remediated home is ready for the patient to move back in.

What HERTSMI-2 does not tell you well: anything about the other 31 species that ERMI covers, the location of a source within the home, or non-Shoemaker-defined health risks. It is purpose-built for the CIRS re-occupancy decision and should not be used as a generic “is there mold here” screen.

Sample collection: same as ERMI, a dust sample from the same lab workflow. Many labs will run the HERTSMI-2 calculation from an ERMI sample at no additional charge.

Cost range in Florida: roughly $250 to $375 standalone, often bundled with ERMI.

Pathways™: peptide-bond protein detection

Pathways™ is a proprietary test methodology developed by EnviroBiomics, Inc. that uses microfiber swabs to collect surface samples and quantifies the total mold-derived protein load at the swabbed location using a peptide-bond detection method. Unlike DNA-based testing, which measures species presence, Pathways™ measures the cumulative protein load that mold has deposited on a surface, including fragments from species that may no longer be viable but whose protein residues remain on the surface.

The methodology is particularly useful for two scenarios. First, identifying contamination pathways, the routes by which fungal material is moving through a building. By sampling multiple surfaces in a structured grid (return air register, supply diffuser, top of door frame, top of light fixture, baseboard adjacent to suspect wall, kitchen exhaust hood, etc.), Pathways™ produces a heatmap that shows where the protein load is highest. That heatmap often points to a hidden source that DNA testing of dust alone would miss. Second, verifying that a remediated building has been adequately cleaned. Because protein residue persists on surfaces longer than viable spores in air, a clean Pathways™ result is a stricter clearance criterion than a clean air sample.

What Pathways™ tells you well: where in the building the cumulative mold protein load is concentrated, regardless of whether the source is still active. It is the test of choice for the “the contractor said it was cleaned but I’m still symptomatic” case.

What Pathways™ does not tell you well: species identification (it measures total mold protein, not species-specific), absolute exposure levels in the breathing zone (it is a surface test), or any non-mold contaminant.

Sample collection: microfiber swabs by a Certified Pathways™ Technician using a structured sampling grid. PureSpec is a Certified Pathways™ provider; see Pathways™ Testing in Florida.

Cost range in Florida: typically $475 to $900 depending on the number of sampling locations.

Conventional spore-trap air sampling

The fourth tool, and the one most people are most familiar with, is conventional spore-trap air sampling. A calibrated pump draws a measured volume of air through a microscope slide impactor cassette over a 5- to 10-minute sample. The cassette is shipped to an accredited laboratory (AIHA-LAP or equivalent) where a microscopist identifies and counts spores by genus or species and reports concentrations in spores per cubic meter.

What spore-trap tells you well: current airborne spore load at the moment of sampling, broken down by genus. Compared against a same-day outdoor reference sample, it identifies indoor amplification, situations where the indoor concentration of a particular genus is meaningfully higher than the outdoor concentration, indicating an indoor source.

What spore-trap does not tell you well: cumulative or historical exposure (it is a 5-minute snapshot), species-level identification for most genera (microscopy generally identifies to genus, not species), or sub-micron fungal fragments that don’t look like recognizable spores under the microscope.

Sample collection: pumps and cassettes operated by the inspector during the site visit. Typical Florida turnaround is 48 to 72 hours.

Cost range in Florida: roughly $150 to $250 per pair of samples (one indoor, one outdoor reference).

The decision matrix

Match the question to the test:

  • “Has this building accumulated water-damage species over time?” → ERMI. Cumulative dust composition is exactly what ERMI was built to measure.
  • “Is this building safe for a CIRS patient to re-occupy?” → HERTSMI-2 with the Shoemaker score ≤ 10 threshold. This is the protocol the CIRS clinical community uses.
  • “The visible work looks clean but I’m still symptomatic, what did the remediation miss?” → Pathways™. The protein-pathway map identifies hidden residual contamination that the visible inspection missed.
  • “Is the air I’m breathing right now elevated compared to outdoors?” → Conventional spore-trap with outdoor reference. The 5-minute snapshot answers the acute-exposure question.
  • “What species is growing on this visible patch of mold on the wall?” → Direct surface sample (tape lift or swab) by microscopy or culture. Not ERMI, not HERTSMI-2, not Pathways™.
  • “Did remediation succeed? Can the contractor take containment down?” → Conventional spore-trap air clearance against outdoor reference, as the primary clearance criterion. Post-Remediation Verification in Florida is built around this test.

Common combinations and when to use them

The four tools are not mutually exclusive and the strongest assessments often combine them.

ERMI + conventional spore-trap. A common pairing for an “is something wrong here” investigation. ERMI provides the cumulative dust fingerprint; the spore-trap pair provides the current airborne snapshot. Together they answer both the historical and the current question.

HERTSMI-2 + Pathways™. The CIRS re-occupancy workup. HERTSMI-2 gives the Shoemaker-protocol number that drives the clinical decision; Pathways™ identifies any remaining contamination pathway that needs to be addressed before HERTSMI-2 can pass.

Full panel: ERMI + HERTSMI-2 + Pathways™ + spore-trap. The complex-CIRS case where the patient has been through multiple buildings, multiple remediations, and multiple non-improvements. This is rare but it is the right scope when the cost of an incomplete answer is another six months of symptoms.

ERMI + mycotoxin testing. When the clinical workup includes the possibility of mycotoxin exposure separate from spore exposure. Mycotoxin testing uses urine or surface samples and measures different markers than ERMI.

Florida-specific notes

Several Florida-specific factors influence the choice.

Post-hurricane assessments. A property that took a flood event from Helene, Milton, Ian, or any future storm benefits most from a conventional spore-trap pre-demo assessment followed by ERMI or HERTSMI-2 several months after the rebuild completes. The spore-trap captures the immediate post-storm condition; the ERMI/HERTSMI-2 several months later confirms that the rebuild did not leave a hidden source.

Persistent high humidity. Florida indoor air sits at higher humidity than most of the country, which keeps fungal species active year-round. Spore-trap results in Florida often look “normal” in summer when outdoor counts are also high, the outdoor reference is the critical comparison, and ratios matter more than absolute numbers.

Salt-air HVAC corrosion. Coastal HVAC systems can develop biofilm on corroded evaporator coils that doesn’t produce dramatic airborne counts but does produce a consistent Pathways™ protein signal at the supply registers. Pathways™ is particularly useful for HVAC-amplification cases in coastal markets.

Older inventory. Pre-1980 Florida housing stock often has cumulative ERMI scores that look elevated relative to the EPA reference even with no acute water damage, because of decades of intermittent moisture cycling. Interpretation needs to be calibrated against the construction era.

What I recommend for first-time clients

For most people calling me for the first time, the right starting test is conventional spore-trap air sampling paired with an entire-property visual inspection, moisture-meter survey, and thermal imaging. That combination identifies whether there is a current problem, where it likely is, and whether it warrants escalation. ERMI, HERTSMI-2, and Pathways™ are escalation tools used when the entry-level assessment suggests there is something to dig into.

For CIRS patients or patients under active workup for environmental illness, the starting test is different. The clinician typically requests HERTSMI-2 with a re-occupancy threshold, often paired with Pathways™ for source localization. The order of operations is set by the clinician, not by me; my job is to produce defensible environmental data that the clinician can act on.

Service references and how to schedule

For service-page detail on each test methodology:

To discuss which test or combination is right for your situation, call (321) 324-7756. The pre-test conversation is part of every PureSpec engagement, matching the test to the question is most of the value of working with a state-licensed assessor, not the sample collection itself.

PureSpec performs environmental assessment and testing only. We do not diagnose or treat health conditions and we do not provide medical advice. Test interpretation in a clinical context is the role of the treating physician. This article describes testing methodology and is for general education.