Decontamination of indoor air to reduce the risk of airborne infections: Studies on survival and inactivation of airborne pathogens using an aerobiology chamber

Abstract

Background: Although indoor air can spread many pathogens, information on the airborne survival and inactivation of such pathogens remains sparse.

Methods: Staphylococcus aureus and Klebsiella pneumoniae were nebulized separately into an aerobiology chamber (24.0 m³). The chamber's relative humidity and air temperature were at 50% ± 5% and 20°C ± 2°C, respectively. The air was sampled with a slit-to-agar sampler. Between tests, filtered air purged the chamber of any residual airborne microbes.

Results: The challenge in the air varied between 4.2 log₁₀ colony forming units (CFU)/m³ and 5.0 log₁₀ CFU/m³, sufficient to show a ≥3 log₁₀ (≥99.9%) reduction in microbial viability in air over a given contact time by the technologies tested. The rates of biologic decay of S aureus and K pneumoniae were 0.0064 ± 0.00015 and 0.0244 ± 0.009 log₁₀ CFU/m³/min, respectively. Three commercial devices, with ultraviolet light and HEPA (high-efficiency particulate air) filtration, met the product efficacy criterion in 45-210 minutes; these rates were statistically significant compared with the corresponding rates of biologic decay of the bacteria. One device was also tested with repeated challenges with aerosolized S aureus to simulate ongoing fluctuations in indoor air quality; it could reduce each such recontamination to an undetectable level in approximately 40 minutes.

Conclusions: The setup described is suitable for work with all major classes of pathogens and also complies with the U.S. Environmental Protection Agency's guidelines (2012) for testing air decontamination technologies.

Keywords: Aerobiology; air decontamination; airborne bacteria; airborne pathogens; indoor air quality.