Airborne Fungal Contamination in Air-Conditioning Systems: Effect of Filtering and Humidifying Devices

Abstract

The fungal contamination of air processed by an air-conditioning system can be quite high, depending on the technical features of different parts such as filtering and humidifying devices, as well as on their maintenance. The effect of filtration and humidification by sprayed water on the fungal air content was studied by analyzing the total culturable airborne fungi and four mold genera: Aspergillus, Beauveria, Cladosporium, and Penicillium. In four air-conditioning systems air samples were collected simultaneously on either side of the filters and humidifiers, using four single-stage viable particle samplers, on a malt agar chloramphenicol medium. High-efficiency filters (EU7) and lower efficiency filters (EU4)were compared, with actual efficiency calculated for every genus identified. The concentration levels measured below the high-efficiency filters were significantly lower than that measured above the filters. For the EU4 filters, the differences were not significant for Beauveria and Penicillium. For the latter a release of spores was detected, raising the question of the growth of microorganisms within the filters. The EU7 filter efficiency (80 to 97%) was higher than that of the EU4 filters, ranging from 36 to 70% depending on the fungi. This variability between genera raises the question of how dependent filter efficiency is on the diameter of particles, as stated for inert particles. Finally, the concentration levels below the humidifier were lower than above it. This was related to the low contamination of the water itself (less than 100colony-forming units per milliliter).