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Introduction: The widespread transmission of the SARS-CoV-2 virus has increased scientific and societal interest in air cleaning technologies, and their potential to mitigate the airborne spread of microorganisms. Here we evaluate room scale use of five mobile air cleaning devices. Methods: A selection of air cleaners, containing high efficiency filtration, was tested using an airborne bacteriophage challenge. Assessments of bioaerosol removal efficacy were undertaken using a decay measurement approach over 3 h, with air cleaner performance compared with bioaerosol decay rate without an air cleaner in the sealed test room. Evidence of chemical by-product emission was also checked, as were total particle counts. Results: Bioaerosol reduction, exceeding natural decay, was observed for all air cleaners. Reductions ranged between devices from <2-log per m3 room air for the least effective, to a >5-log reduction for the most efficacious systems. One system generated detectable ozone within the sealed test room, but ozone was undetectable when the system was run in a normally ventilated room. Total particulate air removal trends aligned with measured airborne bacteriophage decline. Discussion: Air cleaner performance differed, and this could relate to individual air cleaner flow specifications as well as test room conditions, such as air mixing during testing. However, measurable reductions in bioaerosols, beyond natural airborne decay rate, were observed. Conclusion: Under the described test conditions, air cleaners containing high efficiency filtration significantly reduced bioaerosol levels. The best performing air cleaners could be investigated further with improved assay sensitivity, to enable measurement of lower residual levels of bioaerosols.
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Introduction: Modern germicidal ultraviolet C (UVC) equipment can deliver automated UV disinfection treatment by predetermined or self-monitoring cycle. Limited information exists about the performance of such UV systems for treating SARS-CoV-2 and other viral contaminants on surfaces. Published studies differ in their approaches due to the absence of an approved test method. Methods: The ability of germicidal UVC irradiation systems to disinfect surfaces at room and cabinet scale was assessed. Test carriers, seeded with bacteriophage Phi6, were irradiated following a new standard test method. Powered air-purifying respirator equipment was then used to introduce a more demanding challenge. Results: Treatments of seeded carriers using UVC cabinets gave Phi6 log reductions up to 4.58 logs, with little difference between systems. Subsequent treatments, with carriers located on respirator ensembles, were similar, despite shadowing effects. Differences existed for various combinations of cabinet and carrier location. The Phi6 log reduction range was slightly wider for carousel systems, with the most exposed carrier positions giving the greatest Phi6 reductions for seeded respirators. Discussion: Cabinets demonstrated similar performance despite different technical specifications, with maximum observed Phi6 reduction indicating a measurable level of efficacy. There was a more obvious difference in performance between the two carousels, where one delivered an almost twofold higher UVC dose than the other, the most likely explanation for observed performance differences. Conclusion: UVC cabinets and carousels demonstrated Phi6 reductions that could augment routine cleaning measures for reusable respirators. In real-world scenarios, germicidal UVC devices could therefore potentially offer benefits for reducing contact transmission from infectious viruses.
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BACKGROUND: A cough is known to transmit an aerosol cloud up to 2 m. During the COVID-19 pandemic of 2020 the United Kingdom's National Health Service (NHS), other UK government agencies and the World Health Organization (WHO) advised people to cough into their elbows. It was thought that this would reduce viral spread and protect the public. However, there is limited peer reviewed evidence to support this. OBJECTIVES: To determine if cough related interventions reduce environmental contamination, protecting members of the public from infection. METHODS: Scientists and engineers at the Health and Safety Executive (HSE) laboratory used a human cough simulator that provided a standardised cough challenge using a solution of simulated saliva and a SARS-CoV-2 surrogate virus; Phi6. Pseudomonas syringae settle plates were used to detect viable Phi6 virus following a simulated cough into a 4 × 4 m test chamber. The unimpeded pattern of contamination was compared to that when a hand or elbow was placed over the mouth during the cough. High speed back-lit video was also taken to visualise the aerosol dispersion. RESULTS AND DISCUSSION: Viable virus spread up to 2 m from the origin of the cough outwards in a cloud. Recommended interventions, such as putting a hand or elbow in front of the mouth changed the pattern of cough aerosol dispersion. A hand deflected the cough to the side, protecting those in front from exposure, however it did not prevent environmental contamination. It also allowed for viral transfer from the hand to surfaces such as door handles. A balled fist in front of the mouth did not deflect the cough. Putting an elbow in front of the mouth deflected the aerosol cloud to above and below the elbow, but would not have protected any individuals standing in front. However, if the person coughed into a sleeved elbow more of the aerosol seemed to be absorbed. Coughing into a bare elbow still allowed for transfer to the environment if people touched the inside of their elbow soon after coughing. CONCLUSIONS: Interventions can change the environmental contamination pattern resulting from a human cough but may not reduce it greatly.