Development of a method for bacteria and virus recovery from heating, ventilation, and air conditioning (HVAC) filters

Abstract

The aim of the work presented here is to study the effectiveness of building air handling units (AHUs) in serving as high volume sampling devices for airborne bacteria and viruses. An HVAC test facility constructed according to ASHRAE Standard 52.2-1999 was used for the controlled loading of HVAC filter media with aerosolized bacteria and virus. Nonpathogenic Bacillus subtilis var. niger was chosen as a surrogate for Bacillus anthracis. Three animal viruses; transmissible gastroenteritis virus (TGEV), avian pneumovirus (APV), and fowlpox virus were chosen as surrogates for three human viruses; SARS coronavirus, respiratory syncytial virus, and smallpox virus; respectively. These bacteria and viruses were nebulized in separate tests and injected into the test duct of the test facility upstream of a MERV 14 filter. SKC Biosamplers upstream and downstream of the test filter served as reference samplers. The collection efficiency of the filter media was calculated to be 96.5 +/- 1.5% for B. subtilis, however no collection efficiency was measured for the viruses as no live virus was ever recovered from the downstream samplers. Filter samples were cut from the test filter and eluted by hand-shaking. An extraction efficiency of 105 +/- 19% was calculated for B. subtilis. The viruses were extracted at much lower efficiencies (0.7-20%). Our results indicate that the airborne concentration of spore-forming bacteria in building AHUs may be determined by analyzing the material collected on HVAC filter media, however culture-based analytical techniques are impractical for virus recovery. Molecular-based identification techniques such as PCR could be used.

Filtration performances of HVAC filters for PM10 and microbial aerosols— Influence of management in a lab-scale air handling unit

“…For example, particulate cake can serve as a protection for microorganisms or as a support for the adsorption of organic matter, which is used as a substrate (Kuehn et al 1991;Li et al 2010). AHU management improves energy saving and indoor air quality criteria by optimizing several factors: filtration efficiency, comfort of occupants, energy consumption, frequency of changing filters, and efficiency/cost balance (Kemp et al 2001;M€ oritz et al 2001;Farnsworth et al 2006). Operation of AHUs can influence IAQ, for example, when ventilation is stopped or reduced during nights, weekends, or holidays.…”

Decontamination of Bioaerosols within Engineering Tolerances of Aircraft Materials

“…The study showed that the sampling device could detect a low microorganism concentration with low power requirements due to the absence of pressure drop inside the EPSS (Han et al, 2010). Farnsworth et al (2006) conducted a study to evaluate the effectiveness of building air handling units and determining whether they can serve as high volume samplers for airborne bacteria and viruses. To test this, they nebulized and injected aerosols into a test facility upstream of a MERV 14 filter.…”

Optimizing the Recovery of Surrogates for Bacterial Bioterrorism Agents from Ventilation Filters

“…This has been accomplished by immersing small filters or portions of filters in a solution of a Tween surfactant in water and agitating by one of the several methods for a suitable time [16,18,19,25,27,28]. Forms of agitation evaluated have included manual shaking [18,28], mechanical shaking [18,19,25], blending [18,27], vortexing [16,19], and ultrasonic vibration [16,18,19].…”

“…Wang et al [16] discovered that ultrasonic vibration after vortexing improved recovery beyond vortexing by itself. Bacteria in the eluate can be analyzed using culture-based methods [16,19,25,27,28] or molecular techniques [9].…”