Optional Supporting Fungal Information and Data from the Laboratory
By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board
Air sampling for fungal spores to help evaluate allergen load in homes and buildings has been common for over half a century. Originally, only a few experts were involved, and they were all trained mycologists and aerobiologists, or acted in conjunction with such experts, usually in research efforts. The data from these studies was generally analyzed quantitatively if the data sets were large enough, or qualitatively by these few experienced investigators. Investigations of single homes or buildings included intensive on-site inspections, and air sample results were interpreted in light of the visual findings.
One of the reasons mycologists and aerobiologists continue to be important members of the investigative team is to aid in putting the fungal information into context with the other sets of data. Fungal data is often difficult to interpret due to many factors. These include that fungi are naturally occurring, their concentrations can vary widely and rapidly, and the multitude of fungal species comprising a diverse set of characteristics that affect how the results should be interpreted. This fungal complexity, combined with simplistic rules of thumb and a lack of consensus about standards has led to a range of interpretations that is incredibly broad, as many of you have no doubt personally observed.
As an entity that generates sets of data that require mycological expertise to be interpreted correctly, we feel an obligation to provide data about fungi that may make it easier, in some situations, for investigative experts to put the fungal sampling results into context with the rest of the investigation. Consequently, in conjunction with several of the original mycologists and aerobiologists that essentially founded the field, along with other engineers and scientists, EMLab P&K has developed two tools to assist investigators in the interpretation of air sampling data. These tools, both optional and free of charge, are the MoldRANGE™ and the MoldSCORE™.
MoldRANGE™ was designed to demonstrate the range over which outdoor spore concentrations can vary by season and geography. The outdoor aerosol is an extremely important background variable against which indoor air sample data must be compared. However, no single outdoor sample is sufficient to characterize the outdoor aerosol at any one place and time. Precipitation, wind, local sources, and many other factors affect the outdoor aerosol, causing it to change from minute to minute. The MoldRANGE™ analyzes the largest outdoor fungal aerosol database currently in existence. Using it, one can evaluate outdoor air sampling data for representativeness compared to many other samples collected in a similar area or during the same season. The data set we use is compiled data from well over one hundred thousand outdoor spore trap samples that have been analyzed by our certified and highly proficient analysts. Although there will be occasional atypical or faulty outside samples submitted to our database, its large size ensures that the data resulting from these events appear as outliers, and do not significantly affect the reported medians or reported recovery frequency. MoldRANGE™ is not a substitute for on-site outdoor samples, which is why the report cannot be generated without an actual outside sample from the project in question. Nor is MoldRANGE™ a substitute for expert observations of the site. It does, however, provide additional information about typical outdoor spore concentrations, and allows more informed judgments about individual outdoor sampling data means. Further, there are going to be those times when the outside concentration of 'normal' spore types, such as Cladosporium, is below the detection limit. In these cases, simplistic interpretation of inside to outside ratios may well lead to inappropriate conclusions, especially by the partially informed home owner. In these cases, where the expert onsite knows that the data is being interpreted incorrectly, MoldRANGE™ can provide unbiased data to aid in communicating this fact to the homeowner and be an important tool in preventing thousands of dollars of unnecessary remediation.
MoldSCORE™ was designed to quantify the way our experts compare indoor and outdoor spore populations. It is a calculation that takes into account indoor/outdoor concentrations of specific fungal spore types, weighting each spore type for the probability of having an indoor source. It allows for errors due to low indoor and outdoor spore concentrations and to extremely high outdoor concentrations. The resulting score represents the likelihood that a given set of sampling data indicates an indoor source for the sampled aerosols. In the process of developing the MoldSCORE™ we evaluated the many variations of indoor/outdoor ratios that are recommended and used by many. We compared all of these methods to the MoldScore, and to the scores generated directly by our mold experts. None of the indoor/outdoor ratio approaches performed as well as the MoldSCORE™ with respect to false positives and false negatives.
MoldSCORE™ is not meant to be used by itself, since, as many investigators know, both false positive and false negative results are possible with fungal air sampling data. Rather, the MoldSCORE™ is intended to serve as a valuable adjunct to a carefully conducted visual inspection and a well-designed sampling strategy. In many cases, the data collected using these steps will lead to obvious conclusions by the experienced investigator. In more difficult cases, the MoldSCORE™ may be helpful by adding unbiased, mycological experience to the interpretation. In addition, it is an objective measure that will generally support the conclusions of experienced investigators. Where the MoldSCORE™ differs from the investigator's conclusion, the comparison may lead either to a reassessment by the investigator, or to a reassessment of the MoldScore. Both of these events have occurred with the latter serving as a basis for continued development of the MoldScore.
In addition to these tools, EMLab P&K provides statistical calculations based on the methods proposed in the ACGIH Bioaerosols book. Although a study we performed of 100 data sets interpreted by mycologists, engineers, and professional IAQ investigators did not find these methods as representative of an expert's opinion as is the MoldScore, we offer them because they are recommended in such a prestigious publication. EMLab P&K also offers other optional reports such as graphs in a variety of formats to aid in communicating the results to your client, and exports that can be imported into text editing, spreadsheet, or database programs.
Finally, the claim has been made that use of these tools increases liability risk. However, the truth is quite the contrary. The best protection from liability is to do the very best and most complete possible mold investigation. The use of all of the available tools is an important part of that mold investigation. For many mold investigators, the MoldRANGE™ is not necessary since they have accumulated their own large databases specific to the region in which they work. For others it is essential if indoor/outdoor air sampling is to be used. Likewise, the MoldSCORE™ can be an important adjunct in mold investigations, but would never be used in isolation. It is meant to supplement the experienced observations of a good mold investigator, for whom it will almost always provide confirmatory data. If the MoldSCORE™ is not confirmatory, the mold investigator has the option of questioning the reliability of the MoldSCORE, and/or questioning his/her own observations. There are no simple answers to fungal aerosol data interpretation, and the use of air sampling and adjunct interpretation approaches should be restricted to those occasions where it is essential to test a specific hypothesis.
This article was originally published on July 2009.