American Society of Microbiology Evaluation Criteria – Review
When attempting to interpret fungal air sampling data, the question arises – What is the airborne concentration at which the risk of fungal infection is increased?
In 2003, the American 
Society of Microbiology (ASM) published recommendations related to fungal levels for highly filtered patient areas, or Protective Environments [1]. The ASM recommendation can be summarized as follows
- The total fungal pathogen level for HEPA filtered Protective Environments should be not exceed 0.1 Colony Forming Unit per cubic-meter (CFU/m³).
- For plates incubated at room temperature (25° C), the total fungal levels should not exceed 15 CFU/³.
- For plates incubated at 37° C, the total fungal level should not exceed 2 CFU/m³.
Research
Findings from several studies have correlated airborne fungal concentrations among immunocompromised patient populations to the disease incidence rate. For example, Arnow et al. found an increase in the average airborne concentration of Aspergillus species from less than 0.2 CFU/m³ to more than 1 CFU/m³ was accompanied by a 400% increase in the incidence of Aspergillosis (3.5%) [2]. Rhame et al. described a higher risk of Aspergillosis when the average concreteness of A. fumigatus was above 0.9 CFU/m³ [3]. Other researchers have noted similar correlations between environmental fungal contamination and incidence of Aspergillosis [4-6].
Sampling Media
The type of sampling media employed for a survey depends on the purpose of the survey. DG-18 media tend to culture species of Aspergillus and Penicillium better than Malt Extract Agar (MEA). MEA media is well suited for a variety of fungal organisms, including Cladosporium, and Rhizopus (among others). Cellulose media generally have an increased selectivity for organisms with a high water activity, such as Aspergillus fumigatus.