Seasonal Variability of Culturable Fungal Genera in the House Dust of Inner-City Residences

Abstract

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.

Keywords:

• fungal concentrations
• fungal genera
• house dust
• longitudinal study
• repeated measurements
• seasonal variability

ACKNOWLEDGMENTS

This research was supported by Health Homes Technical Study Grant MNLHH0122-03 from the U.S. Department of Housing and Urban Development. We are especially grateful to our participant families and HARS field study staff.

Notes

^A At least one colony of a given fungal genus was isolated.

*p < 0.05 compared with referent season, Winter.

^A Spring (March 20–June 20), Summer (June 21–September 22), Fall (September 23–December 21), Winter (December 22–March 19).

*p < 0.05 compared with any other season.

^A Antilog of means and standard errors in a generalized linear model.

*p < 0.05.

^A Antilog of least squares mean of a fixed effect of season, after adjusting for the effect of intervention in the model that accounted for within-home correlation, compared with referent group (winter).

^B General linear mixed-effects models fit to fungal genera.

^C General linear models fit to fungal genera.

^A Ratio of the within-home variance to between-home variance estimated using a mixed-effects model or a general linear model after adjusting for the effects of intervention (no prior intervention, prior cleaning, prior education, and prior cleaning and education) and season: Spring (March 20–June 20), Summer (June 21–September 22), Fall (September 23–December 21), Winter (December 22–March 19).

^B Mixed-effects model.

^C General linear model.