A volumetric study of winter fungus prevalence in the air of midwestern homes.

Volumetric recoveries of airborne, mesophilic microfungi were made during winter months at three specific points in 150 single-family dwellings in southeastern Michigan. Mean levels of total isolates/m3 comprised a range of from less than 10 to over 20,000, although concurrent outdoor levels never exceeded 230/m3. Form species of Penicillium, Aspergillus, Cladosporium, and Rhodotorula as well as non-pigmented yeasts were the types encountered most widely indoors. Certain homes showed high recoveries of other types, including Cephalosporium, Sporobolomyces, Verticillium, and Sporothrix form species. A positive association between indoor fungus prevalence and bedroom relative humidity was strongly suggested, and high levels were observed in well-humidified homes despite the presence of electrostatic air cleaners. The data indicate characteristic patterns of (winter) air spora in specific homes and suggest that humidifying devices may serve as dispersion sources in addition to their permissive role in facilitating fungus growth.