Indoor health: background levels of fungi.

There is no uniformity in the suggested guidelines for acceptable levels of fungi in indoor ambient air. Thus, health professionals have no way to determine what levels of fungi may pose a threat to human health. The authors reviewed the published literature to identify data reported for noncomplaint structures, that is, structures in which occupants did not have health concerns associated with the quality of the indoor air. For both commercial and residential structures, fungal concentrations detected were often higher than currently suggested guidance values. The average indoor air concentration in 149 noncomplaint commercial buildings was 233 colony forming units (CFU) per cubic meter, whereas outdoor ambient air levels averaged 983 CFU/m(3). Total indoor spore counts ranged from 610 to 1040 spores/m(3) in three commercial buildings. Outdoor total spore counts associated with these buildings ranged from 400 to 80,000 spores/m(3). The average indoor concentration reported for 820 noncomplaint residential structures was 1252 CFU/m(3) with an average outdoor level of 1524 CFU/m(3). Total spore counts detected indoors at 85 residential structures ranged from 68 to 2307 spores/m(3). Outdoor spore levels associated with these structures ranged from 400 to 80,000 spores/m(3). A large proportion of both commercial and residential noncomplaint structures have indoor ambient air fungal concentrations above 500 CFU/m(3), a level often advocated as requiring remediation in structures when occupants complain of nonspecific adverse health symptoms.