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Evaluation of bioaerosols in elementary school classrooms in a coastal temperate zone Bartlett, Karen Hastings

Abstract

Potential determinants of exposure to culturable airborne fungal and bacterial aerosols and carbon dioxide were examined as an aid to the interpretation and evaluation of indoor air quality assessments. Concentration measurments for culturable bioaerosols and CO2 were evaluated against published standards and guidelines. METHOD: All 39 schools from one British Columbia school district were enrolled in the study to ensure different building ages and construction materials, but the same maintenance protocols, were included. Schools were randomly assigned to winter, spring or fall sampling. Data collected included: number of occupants and patterns of occupancy, CO2 levels, temperature and relative humidity, total suspended particles, and air exchange rates using tracer gas (SF6) decay. Other characteristics of the classrooms included the presence or absence of forced air heat, carpets, live animals or aquaria, plants, and the siting of the school or portable classroom. Culturable indoor and outdoor aerosols of fungi and bacteria were collected. Determinants of exposure were modelled by constructing multiple linear regression equations for indoor fungi, indoor bacteria and indoor carbon dioxide. RESULTS: The multiple regression models were able to explain a considerable proportion of the variance for the outcomes of interest (total R2 = 0.59 for mesophilic fungi, 0.61 for bacteria, and 0.68 for CO2). Increased outdoor temperature and outdoor fungal counts were associated with higher concentrations for indoor fungi. Variables describing ventilation and conditions of occupancy were significant to all outcomes of interest but functioned differently in the models. For example, fungal concentration was higher in the presence of natural ventilation, but lower with increased mechanical ventilation. In contrast, CO2 was lower with both ventilation types, and lower with higher outdoor temperature. CONCLUSIONS: Using variables measured during an indoor air quality investigation, predictive models can be constructed which are useful in identifying determinants of bioaerosol and bioeffluent concentrations. Ranges of bioaerosol and bioeffluent concentrations for high occupancy buildings in a coastal temperate zone may differ from guidelines written for other indoor settings and climate zones.

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