A quantitative method to assess the role of indoor air decontamination to simultaneously reduce contamination of environmental surfaces: testing with vegetative and spore-forming bacteria

Abstract

Indoor air can spread pathogens, which can be removed/inactivated by a variety of means in healthcare and other settings. We quantitatively assessed if air decontamination could also simultaneously reduce environmental surface contamination in the same setting. Two types of vegetative bacteria (Staphylococcus aureus and Acinetobacter baumannii), and a bacterial spore‐former (Geobacillus stearothermophilus) were tested as representative airborne bacteria. They were separately aerosolized with a Collison nebulizer into a 24‐m3 aerobiology chamber and air samples collected with a programmable slit‐to‐agar sampler. Settling airborne particles were collected on culture plates placed at, and collected from, five different locations on the floor of the chamber with a custom‐built remote plate‐placement and ‐retriever system. Experimentally contaminated air in the chamber was decontaminated for 45 min with a device based on HEPA filtration and UV light. The plates were incubated and CFU counted. The device reduced the viability levels of all tested bacteria in the air by >3 log10 (>99·9%) in 45 min. Based on two separate tests, the average reductions in surface contamination for S. aureus, A. baumannii and G. stearothermophilus were respectively, 97, 87 and 97%. We thus showed that air decontamination could substantially and simultaneously reduce the levels of surface contamination in the same setting irrespective of the type of pathogen present. Significance and Impact of the Study The innovative and generic test protocol described can quantitatively assess the reduction in environmental surface contamination from microbial decontamination of indoor air in the same setting. This added advantage from air decontamination has implications for infection prevention and control in healthcare and other settings without the need for additional expense or effort. Continuous operation of an air decontamination device, such as the one tested here, can lead to ongoing reductions in pathogens in air and on environmental surfaces.

Biocontamination of surfaces in controlled environment rooms: The influence of environmental parameters and the design of the air conditioning system

“…10,11 Our results showed a positive correlation between bacterial CFUs in the air and on the floors and HCSs, both in the discharge outlet and at the centre of rooms, probably due to the deposit of the first over the second, which corroborates that there is a continuous interaction between the air and surfaces. 16,18,35 In this study, CFUs of bacteria on surfaces were not found in 44% of floor samples and in 63.6% of HCSs. When CFUs were present, 75% of floors had less than 12 or 39 CFU/100 cm 2 , and less than 2 or 6 CFU/100 cm 2 of bacteria on HCSs (with and without a terminal HEPA filter, respectively).…”

“…A continuous interaction between air and surfaces exists, 16,17 as particles are deposited on surfaces and subsequently resuspended. 18 Bacterial survival in the air is correlated to indoor environment and design parameters (air filter, the direction of airflow, air pressure, air changes per hour (ACH), humidity, temperature).…”

Should homes and workplaces purchase portable air filters to reduce the transmission of SARS-CoV-2 and other respiratory infections? A systematic review

“…Some commercially available air filters have been tested within experimental chambers, designed to replicate bioaerosols in an indoor setting. One study conducted in Canada in 2018 replicated specific bioaerosols to determine the effectiveness of a filter in reducing surface contamination [ 20 ]. The experimentally contaminated air was filtered using a portable device which combined HEPA filtration and UV light.…”

A Systematic Literature Review of Indoor Air Disinfection Techniques for Airborne Bacterial Respiratory Pathogens

“…Few studies have assessed the combination of UV-C and other disinfection methods. When HEPA filtration was combined with UV, the system reduced more than 99.9% of viable airborne Klebsiella pneumoniae, Acinetobacter baumannii, and S. aureus after 45 min of operation in an aerobiology chamber [59,60]. An ultraviolet photocatalytic oxidation (UV-PCO) scrubber showed 3.5 to 5.3 log reduction of airborne Enterococcus faecalis with one UV lamp operating (average UV irradiation 6595 µW/cm 2 at a contact time of 1 s) and a 7.5 log reduction with two lamps operating, although it should be noted that the irradiation varied markedly depending on proximity.…”