Evaluation of children as sources of bioaerosols in a climate chamber study

Abstract

Emissions of viable particles from a group of children were measured under controlled conditions in a climate chamber that simulated indoor environmental exposure in day-care institutions with tight building envelopes and outdoor air supply by natural infiltration only. Bioaerosol sampling was simultaneously applied with slit samplers and sediments plates. A total of 142 strains was identified. Most of these were from sediment plates (95%) as the colonies on the slit sampler were more crowded and too confluent for separation. On sediment plates, coryneform bacteria dominated (27–85%), followed in frequency by micrococi (4–50%), Staphylococcus epidermidis and saprophyticus (12–43%), Bacillus spp., most frequently B. megaterium (12–33%), and Acinetobacter spp. (11–14%). From the slit sampler plates, staphylococci dominated (67%), followed by coryneform species and micrococci (17%). Within the first hour after the group left the chamber, the number of colony forming units (CFU) suspended in the air decreased, corresponding to an equivalent dilution ventilation rate of 2.0 ACH (air changes per hour) for bacteria and 1.7 ACH for mold spores due to the catching of particles on surfaces and to die away of viable microorganisms. Accordingly, microbial surface contamination revealed an increase at the same time.