Evaluation and Determinants of Airborne Bacterial Concentrations in School Classrooms

Abstract

A survey of 39 elementary schools was undertaken to determine indoor air concentrations of bioaerosols within a coastal, temperate climatic zone in British Columbia, Canada. This article reports the results for airborne bacteria. Determinants of exposure were grouped into environmental (outdoor temperature, relative humidity, season, weather), ventilation and comfort parameter (indoor relative humidity, temperature, indoor CO2 concentration, indoor fungal concentration), and occupancy (number of occupants, activity levels, occupancy patterns) variables. Regression modeling was used to evaluate the association between these factors and measured concentrations of indoor mesophilic bacteria. Naturally ventilated rooms (47% of the total rooms surveyed) had higher bacterial counts than mechanically ventilated rooms (geometric mean 325 vs. 166 CFU/m3, respectively, p < 0.001). In univariate analyses, bacterial counts were negatively correlated with supply and exhaust flow rates, air exchange rates, and the percentage of the day that occupants spent quietly sitting at their desks. Analysis of bacterial groups indicated various sources of the bacterial aerosol, with micrococci and staphylococci closely associated with occupancy variables, Bacillus with site and occupancy, and coryneform bacteria with site variables only. Approximately 60% of the variance in the outcome measurement of total bacteria was accountedfor by indoor CO2, lower air exchange rate, the age of the building, signs of current or old moisture stains, room volume, indoor relative humidity, and occupant activity level in a multiple linear regression model, with ventilation factors accounting for 40% of the variance.

Seasonal and Diurnal Variability in Airborne Mold from an Indoor Residential Environment in Northern New York

“…This variation in mold activity (spore production) could be because of rapidly growing mold sources or varying environmental conditions between days. Percent relative uncertainty for daily indoor mold samples in summer ranged from 7 to 36%, which is in agreement with the fungal concentration variability of 15.3% found in school classrooms by Bartlett et al 33 Percent relative uncertainty for daily indoor mold samples in winter ranged from 24 to 212%. IAQ practitioners should consider these coefficients of variation as an estimate of the uncertainty in single-day sampling strategies.…”

Indoor Air quality related to occupancy at an air-conditioned public building

“…Epithelial and mucosal surfaces are colonized with bacteria, microflora that become liberated through the normal shedding of skin cells or though aerosolization from mucosal surfaces by talking, coughing or sneezing. High concentration of bacteria contributed by room occupants influenced the air quality independent of an infectious disease (Bartlett et al, 2004). The geometric mean indoor concentration of airborne bacterial was 541 CFU/m 3 ranging from 110 to 1955 CFU/m 3 .…”

“…Presently, there is no sufficient information on dose-exposition relationships regarding viable and cultivable biological agents (Dacarro et al, 2003). Despite the intense interest in the role of bioaerosols to health, there is no consensus for regulatory limits on airborne bacterial concentrations in indoor air (Bartlett et al, 2004). A significant correlation between occupant density and indoor bacteria concentration support the future application of using bacteria levels as an indicator for indoor-originated contamination.…”

Assessment of Indoor Bioaerosols in Public Spaces by Real-Time Measured Airborne Particles

“…However, the subsequent conventional microbiological cultivation takes 3-5 days to obtain biological pollutant concentrations at the sampling site, which may delay the response to poor IAQ. Although conventional microbiological culture methods are unable to measure the concentration of biological pollutants in real time, there have been numerous studies investigating the correlation of indoor bioaerosols with indoor and outdoor air and environmental parameters, such as ventilation, house age, number of indoor personnel, temperature, relative humidity, wind speed, CO 2 , and sizesegregated particle number concentrations (total, ultrafine, and submicron particle number concentrations), and particle mass concentrations (PM 2.5 and PM 10 ) (Goh et al, 2000;Luoma and Batterman, 2001;Hargreaves et al, 2003;Zhu et al, 2003;Agranovski et al, 2004;Bartlett et al, 2004;Tseng et al, 2011;Raval et al, 2012;McDonagh et al, 2014).…”