FUNGAL PROPAGULES IN-HOUSE DUST .1. COMPARISON OF ANALYTIC METHODS AND THEIR VALUE AS ESTIMATORS OF POTENTIAL EXPOSURE

The presence of viable mold propagules in house dust was investigated by 10 different analytic methods, in order to determine to what extent different results are obtained when different analytic methods are used. Moreover, the Value of this measurement as an estimator of the potential exposure to fungi in epidemiologic studies was assessed. Floor and mattress dust was sampled in 60 homes in The Netherlands during autumn 1990. For investigation of the variability in time, sampling was repeated in 20 homes after 6 weeks. Each analytic method is characterized by a unique combination of culture medium, suspension medium, and dilution step. The highest mean number of colony-forming units (CFU)/g dust was obtained by suspension of at least 100 mg dust in a peptone or sucrose solution in a ratio of 1:50 (w/w), followed by 10-fold dilution and plating on DG18 agar (geometric mean (GM) approximately 60 000 CFU/g dust). The lowest mean number of CFU/g dust was obtained by direct plating of 30 mg dust on V8 agar (GM approximately 5300 CFU/g dust). The mean coefficient of variation of duplicate analyses varied from 11%, for suspension in sucrose and plating on DG18 agar, to 27%, for suspension and dilution in sucrose in combination with V8 agar. The highest mean number of species isolated was obtained by direct plating of 30 mg dust on DG18 agar (mean number of species: 17). Suspension and dilution on DG18 or V8 agars yielded an average of approximately six species. In duplicate analyses, the mean percentage of agreement for the species isolated varied from approximately 35%, for suspension and dilution, to 60%, for direct plating. The reproducibility of the number of CFU/g dust in time was better for mattress dust than for floor dust; however, also for mattress dust, the predictive value of a single measurement was rather low. The variability in time in species isolated was substantial, both for mattress dust and floor dust. We concluded that results of measurements of viable mold propagules in house dust, both quantitatively and qualitatively, depend greatly on the analytic methods used. Furthermore, a single measurement of fungal propagules in settled house dust does not provide a reliable measure of potential exposure to fungi in indoor environments.