There are currently no published standards for many IAQ laboratory methods. In fact, due to the lack of a standard method for
the analysis of fungal spores in indoor air, there is a diverse range of analytical approaches and statistical analysis of data.
Laboratories typically analyze anywhere from 15% to 100% of the sample for spore trap cassettes and depending on the nature of
the sample, the percentage analyzed can have a significant effect on the final results.
A study was conducted to identify significant differences, if any between two common analytical approaches for spore trap
cassettes. Fifty-five Zefon Air-O-CellŪ cassette samples were analyzed via both the 15% and the 100% counting method and the
results compared. These samples, which were taken in various indoor and outdoor environments, were analyzed by degreed analysts
with at least two years experience. The results were compiled and several interesting observations were made when comparing the data.
In outdoor air samples the data shows relatively little influence on method selection. In sharp contrast, air samples from
indoor environments often contain aggregate fungal conidia and other multi-spore structures; the data shows significant differences
between the two methods.
When compared to reading 100% of the sample, the 15% technique failed to detect Stachybotrys in nine percent of the samples.
The 100% counting method detected at least one Stachybotrys spore in 5 of the samples analyzed, whereas the 15% method detected
zero Stachybotrys in the entire project. With Stachybotrys and other specific moisture indicator genera commonly being a target
of interest in both analysis and remediation efforts, it would be beneficial to use a 100% counting method.
In addition, eighteen percent of the samples were skewed due to heterogeneous deposition of spores. Samples with few chains or
clumps of spores that were detected on the 15% technique, when calculated, made a huge impact on the final results. For example,
when a chain of five Cladosporium spores is detected in the 15% count, the extrapolation is then 467 Cladosporium/m3. The same number
of spores counted with the 100% method is calculated at only 67 Cladosporium/m3. Conversely, if there are a few scattered chains
throughout the sample trace, but only one of these chains is detected in the 15% technique the calculated results will be much higher
(and more accurate) in the 100% counting method.
Samples with low spore concentrations showed variation in results as well. For example, twenty-five percent of the samples missed
five or more genera using the 15% counting method. These samples had between 1 and 25 spores for each of the missed genera counted.
This could easily result in the difference of a zero total spore count using the 15% method and a significant total spore count using
the 100% method.
Using the 15% counting method, nine percent of the samples failed to detect spores in concentrations less than or equal to 227 per
cubic meter. Again, these are low spore concentrations, but the reporting of such results only occurred with the 100% counting method
and may have included Stachybotrys or other key genera.
Selecting a laboratory for IAQ analysis may be a difficult choice, especially with the number of laboratories available. With this
in mind, and in the absence of a standard method for spore trap analysis, it is advisable to look at the benefits of using a laboratory
employing the 100% counting method. Heterogeneous spore deposition on an indoor slide, low spore concentrations and the difference between
a 100% counting method as opposed to a 15% counting method can make all the difference in the world when accuracy is of the utmost importance.
