Is the Spore Trap Obsolete for Indoor Mold Testing?

The spore trap type air sampling cassette is a sampling device designed for the rapid collection and analysis of a wide range of airborne aerosols. These include fungal spores, pollen, insect parts, skin cell fragments, fibers, and inorganic particulates. Air enters the cassette, the particles become impacted on the sampling substrate, and the air leaves through the exit orifice. The airflow and patented cassette housing are designed in such a way that the particles are distributed and deposited equally on a special glass slide contained in the cassette housing called the “trace.” Benefits: Useful for initial site testing, especially if fungal growth is not visible.

Disadvantages of the Spore trap method:

 

  • Fungi cannot be fully speciated with this method. For example, Aspergillus sp. and Penicillium sp. are normally reported together due to the similarities in B+ Cubensis Spores morphology.
  • Spore viability cannot be assessed, as it is not possible to differentiate between viable and nonviable
  • Sampling method is cumbersome and noisy
  • Large lab-to-lab variation in identification
  • Methodology not accepted by all within the industry

 

So what if spore traps can’t tell species’ differences?

Since many water-intrusion molds look the same in a microscope, a spore trap analysis can’t provide species differentiation. Thus, a comparison of indoor and outdoor samples won’t provide information on the real differences between samples, only TOTAL counts of spores that appear similar. Therefore, if a given indoor sample has the same total counts as an outdoor sample but the species are different, the inspection would likely miss a moisture-related mold problem. This is because a spore traps ASSUMES that the species variations are the same from a given set of indoor and outdoor samples. Remember: A spore trap count will not identify different species of Aspergillus or Penicillium in a set of indoor and outdoor samples.

Don’t spore traps collect spores in the size range of most water-intrusion molds?

No. The spore trap is an impaction collector. The collection efficiency of a spore trap is depending upon both the air flow rate and the physics of impaction. In short, spore traps do not capture fungal spores below 3 to 4 microns in diameter. This means that most species of molds of Aspergillus and Penicillium are collected at very low rates in standard spore traps compared to larger molds. This phenomenon is a widely known but little-discussed fact in the laboratory community.

So how can we optimize collection?

To collect virtually all mold spores, the collection method must collect spores of all sizes. Ideally, a filter-type collector where air is collected and sampled through a porous medium should be used. Newly developed systems just now being introduced into the market makes this option practical. In one version, the EmTrap, the air sample is pulled through a membrane filter with 0.8 micron nominal pore size. Thus, unlike for spore traps, almost all intact spores collected through the filter will be captured.

So if the EmTrap solves the “small spore size” issue, why would I need to perform the more expensive MSQPCR analysis?

Remember that a spore count is not the same as a spore species identification. Whether we count spores in a standard spore trap or a SporeLock, we still cannot determine the species as in a MSQPCR. Alternatively, next generation immunoassays are compatible with such filter collection devices and offer an other option for the professional who wishes to test sample themselves on site.

OK, but why should I quantify and determine the species for 36 different molds: The EPA Relative Moldiness Index and Group 1 versus Group 2 molds

Extensive research conducted by the U.S. EPA has established the EPA Relative Moldiness Index, otherwise known by the acronym ERMI. The ERMI score narrows down the total number of critical mold species to 36 indoor-indicator mold species. The 36 species are subdivided into two very different groups of mold (fungal) species, referred to as Group 1 and Group 2 molds. The Group 2 molds are found to be common in most homes and in low concentrations. Occupants living and working in indoor environments that contain predominantly Group 2 molds were healthy and suffered few respiratory related illnesses, nor did the building structures suffer leaks and water intrusion. However, Group 1 molds were much less benign, and occupants of these homes and environments suffered significant respiratory and asthma related illnesses. Moreover, Group 1 molds were significantly correlated to water intrusion due to poor construction or leaking pipes. Furthermore, EPA scientists and other reputable scientific investigators have amassed a body of published scientific research that conveys a major paradigm shift in the way mold samples are both collected and analyzed.

 

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