Seasonal variability of culturable fungal genera in the house dust of inner-city residences.

House dust samples were collected up to six times over a 1-year period to explore seasonal variability of individual fungal genera in inner-city households in Minneapolis, Minnesota. General linear mixed-effects models were used to explore the variability of 13 fungal genera (Cladosporium, yeasts, Aureobasidium, Alternaria, Penicillium, Epicoccum, Mucor, Rhodotorula, Aspergillus, sterile fungi, Phoma, Pithomyces, and Fusarium) found in more than 20% of total dust samples. The five most common fungi (% of samples detected) were Cladosporium (81%), yeasts (63%), Aureobasidium (57%), Alternaria (56%), and Penicillium (55%), with the remaining genera found in 20-50% of the samples. When expressed as frequency of occurrence (%), genus fraction of total fungal concentration (%), or concentration of individual genera (CFU/g), these five genera also varied substantially by season. In contrast, Aureobasidium, Fusarium, and Mucor levels remained relatively constant throughout the year. The observed concentrations of the five most common fungal genera were higher than levels associated with increased respiratory symptoms reported in previous studies. Our results indicate that seasonal variability in common fungal genera is large: within-home to between-home variance ratios of Penicillium (4.1), Alternaria (4.9), Cladosporium (7.1), and yeasts (20.3) were substantially larger than that observed for total fungi (2.5). These results suggest that future studies attempting to link individual fungal genera to health effects need to characterize and control for this seasonal variability.