Evaluation of HVAC filters as a sampling mechanism for indoor microbial communities Federico Noris, Jeffrey A. Siegel, Kerry A. Kinney * Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, C1700 Austin, TX 78712-1076, USA article info Article history: Received 26 July 2010 Received in revised form 7 October 2010 Accepted 8 October 2010 Keywords: Bacteria Fungi Microbial community HVAC filter Settled dust Air abstract HVAC filters are in place for extended periods of time and can serve as integrated air samplers. This paper presents a comparison of bacterial and fungal concentrations and communities in HVAC filter dust and other sampling locations in occupied residences and in the unoccupied UTest House. A DNA-based, culture-independent approach was utilized to characterize the microbial communities. Microbial concentrations and communities in HVAC filter dust samples were not statistically different from those in high surface dust samples in occupied homes. Despite the general similarity in the communities, Proteobacteria were present in greater proportion in HVAC filter dust samples than in surface dust samples suggesting the air origin of this phylum. Gram-positive bacteria were present in greater proportion in occupied residences than in an unoccupied test house, confirming the potential association of this group with occupants. HVAC filter microbial communities were not different from those present in a composited month-long indoor air sample providing preliminary evidence that filters could be a viable option for long-term investigation of airborne biological contaminants. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The presence of microorganisms indoors has been related to several health and discomfort outcomes including respiratory diseases, odors, and occupant dissatisfaction (Gyntelberg et al., 1994; Verhoeff and Burge, 1997). Some researchers have associ- ated indoor microbial concentrations with asthma symptoms (Park et al., 2006; Ross et al., 2000; Smedje et al., 1997). However, the association between culturable fungal levels in air or dust samples and health problems has been inconsistent (Nelson et al., 1995; Peat et al., 1998; Verhoeff and Burge, 1997). This discrepancy may be attributable to the fact that bioaerosol samples are typically short- term in nature and provide only a snapshot of microbial contami- nant levels in air at a particular time and place. Even when collected from the same location, airborne bacterial samples have significant temporal variability (Fierer et al., 2008), highlighting the need to develop an integrative methodology to assess indoor biological contaminants. Floor dust may provide an integrated sample of contaminant levels but these samples are influenced by material tracked-in from the outside and may be skewed towards larger particle-bound contaminants (Lewis et al., 1999). The majority of previous indoor biological studies have relied on an assessment of culturable microorganisms that represent only a small fraction of the total microorganisms present indoors (Toivola et al., 2002). In recent years, several studies have applied culture- independent, DNA-based approaches to better characterize the diverse bacterial and fungal communities present in indoor envi- ronments (Kelley et al., 2004; Pakarinen et al., 2008; Pitkäranta et al., 2008; Rintala et al., 2008; Täubel et al., 2009; Tringe et al., 2008). The application of molecular biology tools to indoor environmental investigations should reveal a much greater fraction of the microbial community present than culturable methods, a finding recently confirmed by Pitkäranta et al. (2008). Vesper et al. (2007) reported an association between asthma symptoms and the Relative Moldi- ness Index (RMI), an index based on molecular biology tools, con- firming that these techniques may provide a better characterization of health effects from microorganisms. A potential alternative to the use of settled dust and air samples for microbial evaluation is the use of heating, ventilation, and air conditioning (HVAC) filters for indoor environment investigations. Collecting samples of HVAC dust may improve our understanding of indoor occupant exposure by providing an integrated measure of pollutant concentrations associated with indoor particles. Greater * Corresponding author. The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, Cockrell School of Engineering, ECJ 8.212,1 University Station C1700, Austin, TX 78712, USA. Tel.: þ1 512 232 1740; fax: þ1 512 471 0592. E-mail addresses: fedenoris@mail.utexas.com (F. Noris), jasiegel@mail.utexas. edu (J.A. Siegel), kakinney@mail.utexas.edu (K.A. Kinney). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.10.017 Atmospheric Environment 45 (2011) 338e346