3 3. SAMPLING OF COLLECTION RECOVERY SITES FOR THE LEVEL OF CONIDIAL CONTAMINATION

3.1 3.1 SAMPLING GOALS

The goals of sampling or monitoring for fungal contamination in a building are: (1) to determine if there is a sufficient number or level of conidia to be considered a problem; (2) to identify the species of the fungal conidia to discover if they are a health hazard; and (3) to assist in the location of the source (amplifier) of the conidia.

3.2 3.2 SAMPLING METHODS

The surface sampling of moldy materials for species identification will be done prior to any recovery activity. We know that the moldy objects are the amplifier; thus the concern here is the change in the level of contamination at the recovery site.

3.2.1 3.2.1 Methods

A variety of different methods of air and surface sampling can ascertain conidial contamination. The commonest methods are described and critiqued in a report by Health Canada (1995). Essentially, air sampling may be done by pumping a measured amount of air onto or through a collecting device or by sedimentation (relying on gravity) of the conidia onto settle plates. In both cases the captured conidia are cultured on a growth media, and the results are recorded as colony forming units: CFU/volume of air or CFU/time.

Other methods of air sampling involve the capturing of conidia by pumping air or sedimentation directly onto microscope slides for microscopic identification and counting. These methods do not involve the culturing of the trapped conidia. The results of these methods are recorded as total spore count-nonviable (TSC/volume of air or TSC/time). Even though the term “spore” is used, it is conidia that are counted.

Surface sampling is often done by using sterile cotton swabs to remove conidia from a specific surface area. The swabs may be covered with a nutrient medium, or plain swabs may be washed in a nutrient medium. The nutrient medium is then cultured, and the swab analysis is recorded in CFU/surface area.

Surface sampling is also done by using Scotch tape to remove conidia in dust from contaminated surfaces for microscopic examination and recorded as TSC/surface area.

3.2.2 3.2.2 Biases in CFU Tests

Results recorded as CFU/volume of air, time, or surface area are inevitably biased.

First, because the methods involve only conidia that can germinate and develop subsequent growth, false negatives may occur because some conidia may be dead, not activated and unable to germinate, or unable to utilize the growth medium used. Using several growth media can alleviate some of this bias. Health Canada (1995) suggests that microscopy should be done along with CFU determinations to detect the excluded conidia.

Second, air pumping and sedimentation methods produce a bias because air samples are not homogeneous. The air sampled may involve still air, air drafts, air conditioning air, or air disturbed by human activity.

Third, the settling rate of conidia onto surfaces depends on their weight, size, morphology, and water content. Thus a species with small and light conidia may be in low amounts or excluded from the sedimentation sample while another species with large conidia will be present in biased high amounts. The common Aspergillus and Penicillium species, which are our major concern, are poor settlers because they are small and light.

3.2.3 3.2.3 Biases in TSC/Volume of Air Tests

Results recorded as TSC/volume of air are like wise biased by nonhomogeneous air and settling rates of conidia. Yet the microscopic analysis results give a total of all conidia captured, eliminating the bias due to false negatives. Additionally, staining of conidia with a vital stain can be used to determine if they are viable. The pumping air method with TSC/volume of air gives the most accurate analysis of air (MacRae 1998).

3.2.4 3.2.4 Bias in Surface Sampling

Surface sampling with Scotch tape or swabs removes all conidia present, i.e., the deposition of conidia over an unknown period of time. Yet, conidia that have settled on the surface over years may have nothing to do with the collection recovery activities. In collection recovery it is essential to first test a cleaned surface to obtain a reference point that can be compared to samples taken during recovery activities.

3.3 3.3 INTERPRETATION OF TEST RESULTS

The biases described above limit our ability to determine when we have a fungal growth problem. Health Canada (1995) points out that even if conidia concentrations in room air were known with absolute accuracy, we would be little further ahead in understanding the association between these numbers and allergic or respiratory symptoms. In addition essential dose-response information to correlate numbers of fungal conidia of particular fungal species to health effects in humans is absent for all molds, and as tolerances in individuals vary so greatly, acceptable dose-response data continue to be very difficult to obtain.

Because of the biases in sampling and the difficulty in the assessment of the problems, I have come to the conclusion that the only logical approach during cleaning of moldy archival material or artifacts in collection recovery sites is to strive for aseptic technique, a preventive approach.