Airborne fungal and particle mitigation in HVAC systems - An evaluation trial in a coastal healthcare facility.

Exposure to airborne fungi can lead to serious health outcomes for vulnerable hospital patients, especially where the facility is situated in a humid environment. Moist conditions can lead to fungal colonisation within air conditioning systems (HVAC), particularly centralised ducted systems such as those typical within healthcare applications. Advanced air cleaning systems can potentially provide both filtration of airborne fungi and decontamination. The primary aim of this study was to compare the performance of a traditional mechanical filter with an advanced air cleaner with multiple modes of bioaerosol mitigation (AMAC). An intervention trial was conducted in a healthcare facility in a semi-tropical location where there is also the potential for seawater aerosol impaction adding to moisture load. Airborne fungi and size-resolved airborne particles were monitored at various points in the air handling unit (AHU) and supply ducts, before and after the installation of the new air cleaner (first intervention). Filter cartridge air sampling coupled with light microscopy were used to determine airborne fungal concentrations and broad taxonomic profiles. Common fungal types found were Cladosporium, Aureobasidium, Aspergillus- and Penicillium-like structures, often associated with fungal growth in HVAC systems. Post AMAC installation, filtration efficiency rose from 86.7 to 99.9%. However, total airborne fungal structure concentrations (TAFSC) increased as air left the AHU (rising from 1 to 22 fs/m3) and further at the Nurse Unit Manager's office supply air register (NUMSAR, 387 fs/m3). This was consistent with inspection and surface testing of duct contamination downstream of the AHU filter. Following subsequent duct replacement and cleaning of contaminated surfaces (second intervention), TAFSC at the NUMSAR were lowered further to 171 fs/m3. Concentrations of Aspergillus/Penicillium spp. reduced significantly from 151 to <1 fs/m3 and Cladosporium spp. levels fell from 84 to <1 fs/m3. The findings suggested an original potential source and/or temporary reservoir of key dampness-related genera in the HVAC system. Real time monitoring of undifferentiated airborne particle concentrations followed a similar trend to fungal concentrations. Unlike the mechanical filter, the AMAC performance appeared to be independent of relative humidity within the observed range. Healthcare facilities, especially in locations subject to elevated humidity or high rainfall events, may consider high performance air cleaning as a key strategy for reducing health risks in healthcare settings.