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Evaluation of Culturable Particle Load on HVAC Filters Before and After Remediation: A Pilot Study

Department of Environmental and Occupational Health, Drexel University School of Public Health, Philadelphia, PA, USA, hrp22{at}drexel.edu

Neil J. Zimmerman

School of Health Sciences, Civil Engineering Building, 550 Stadium Mall Drive, Purdue University, West Lafayette, Indiana, IN, USA

Zekarias Berhane

Department of Epidemiology and Biostatistics, Drexel University School of Public Health, Philadelphia, PA, USA

This pilot research was performed to evaluate a quantitative method for culturing particles on HVAC filters. The reasons were to compare relative concentrations of culturable fungi found in two separate rooms of a six-floor building and to re-evaluate culturable fungi in the same building after remediation efforts. The evaluated quantification method involved shaking samples of filter materials in sterile saline followed by plating out.

The pilot study consisted of two phases. Firstly, a case study comparison of two HVAC filters from a building with a history of indoor air quality concerns in the space served by one of the filters. The second, following remediation efforts in the same building. This involved the quantification of culturable fungal particles on each of ten filters serving ten separate areas of the building. Statistical analysis of the phase I results indicated a significantly greater number of viable particles on the complaint filter than on the non-complaint filter following culture and quantification on either malt extract agar (p=0.02) or potato dextrose agar (p=0.03). Phase II results suggested a factor of four decrease in culturable fungal load following remediation.

This limited study was performed for preliminary assessment of the use of a filter quantification method to estimate relative airborne fungal load. The results suggest that more work is merited but limitations in the scope of the research and the statistical power of the analysis mean further conclusions regarding method efficacy cannot be drawn.

Key Words: fungi and HVAC filters • mould • indoor air quality • fungal sampling

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