INTERPRETING MOLD RESULTS

Since there are no established threshold limits for mold in an indoor environment, much care and consideration must given to the interpretation of testing results. When taking air samples, a sample or samples from outdoors should be taken to serve as a reference for comparison with indoor air. It may also be helpful to take samples from non-complaint areas to serve as indoor references.

In general, the concentration of organisms in indoor air should be lower than that of outdoor air samples. Also, the concentration of organisms from non-complaint areas should be lower than that of complaint areas. Generally, the same types of organisms should be found indoors and outdoors. If there is a difference in the microbial diversity between indoor and outdoor samples, this may be an indication of indoor amplification. It should also be noted if the presence of indicator organisms is detected. These are organisms that are associated with water-damaged materials or high humidity. Some indicator organisms include: Acremonium sp., Aspergillus (some species), Chaetomium sp., Eurotium sp., Fusarium sp., Memnoniella sp., Penicillium (some species), Stachybotrys chartarum (synonym S. atra), Trichoderma sp., Ulocladium sp., and Wallemia sp.

The confirmed presence of Stachybotrys chartarum in an indoor environment requires urgent risk management decisions to be made due to the potential high toxicity of this organism. For further information on the handling of this organism consult "Guidelines on Assessment and Remediation of Fungi in Indoor Environments" (available through the New York City Department of Health web site at: http://home2.nyc.gov/html/doh/html/epi/moldrpt1.shtml). Also, careful consideration should be given to organisms that are known to cause disease, especially in immunocompromised individuals: Aspergillus fumigatus, A. flavus, A. niger, A. versicolor and Fusarium moniliforme as well as some of the Zygomycetes. These should be given special attention in hospital settings or areas occupied by individuals with impaired immune system function.

Tape lift samples:

• These results are generally qualitative.
• This method is used to confirm suspected visible growth.
• Results are reported as a relative amount of spores on a gradient scale:
     Massive > Numerous > Many > A Few > Trace > No Growth
• Massive, Numerous, and Many may indicate active fungal growth; whereas, A Few and Trace may indicate background or minor contamination.

Swab samples:

• These results are semi-quantitative.
• This method is used to confirm suspected visible growth.
• Results are reported as Colony Forming Units (CFU)/ unit area.

Bulk samples:

• Direct microscopy or culturing can be performed on bulk samples.
• This method is used to confirm suspected visible growth.
• For direct microscopy, results are reported the same as tape lift samples.
• For cultures, results are reported as CFU/gram of material.

Dust samples:

• Direct microscopy or culturing can be performed on dust samples.
• This method is used to detect growth in dust found on surfaces, in carpets, or in fabrics.
• For direct microscopy, results are reported the same as tape lift samples.
• For cultures, results are reported as CFU/gram of dust.

Spore Trap samples (Air-O-Cell, cyclex-d, Allergenco, etc.):

• This method is used to detect the presence of airborne mold spores (viable and non-viable).
• Identification is performed to genus level when possible or group.
     (Aspergillus and Penicillium spores are similar and are reported together)
• Compare results of indoor vs. outdoor samples and complaint vs. non-complaint areas.
• Results are reported as Fungal Structures/m³ of air.
• Non-microbial particulate levels may mask fungal structures, giving false low counts. The non-microbial particulate levels are rated as follows:
• Low: 0-25% of slide covered, this may show slightly decreased counts.
• Moderate: 26-75% of slide covered, actual counts may be from 1-4 times higher than reported.
• Heavy: >75% of slide covered, actual counts may be from 4 - 10 times higher than reported.

Culturable Air samples:

• This method is used to detect the presence of viable airborne mold spores.
• Identification is performed to genus level and species level when appropriate and possible.
• Compare results of indoor vs. outdoor samples and complaint vs. non-complaint areas.
• Results are reported as CFU m³ of air.