Contributions of Foot Traffic and Outdoor Concentrations to Indoor Airborne Aspergillus

Aspergillus is amold genus that can cause allergies, asthma, and pulmonary infections in sensitive people; its particles are common in indoor air. Two potential contributors to indoor Aspergillus particles were examined in this field study: human activity (walking over carpet), and outdoor Aspergillus concentrations. Filtered air samples were collected outdoors and inside two carpeted hallways in public buildings, while measuring indoor foot traffic. Aspergillus concentrations were analyzed using quantitative Polymerase Chain Reaction (qPCR). A bivariate model was used to predict indoor Aspergillus concentrations based on foot traffic and outdoor Aspergillus concentrations. For 3 of 4 scenarios, most of the variation in indoor Aspergillus could be explained by the combined effect of outdoor Aspergillus concentrations and foot traffic, with particularly strong correlations during peak traffic times. In addition, indoor Aspergillus was significantly associated with outdoor Aspergillus in 2 of 4 scenarios, and with foot traffic in 2 of 4 scenarios. For 2 of 3 sampling campaigns, Aspergillus did not have a significant association either with gravimetric particulate matter <= 5 mu m (PM(5)), or with optically measured PM of 0.75-1 mu m, 1-2 mu m, 2-3.5 mu m, or 3.5-5 mu m. Controlled experiments, examining whether the foot traffic contribution was due to resuspension from carpeting or to shedding from clothing and/or human bodies, saw a significant increase in Aspergillus levels from resuspension. Although an increase was also seen for clothing over Tyvek suits, it was not statistically significant.