Viable Virus Aerosol Propagation by PAP Circuit Leak and Mitigation with a Ventilated Patient Hood – A Model for Improving Health Care Worker Safety in the COVID-19 Pandemic

Background: Nosocomial transmission of SARS-CoV-2 has been a major cause of morbidity and mortality in the COVID-19 pandemic. Emerging evidence suggests patients auto-emit aerosols containing viable respiratory viruses. These aerosols could be further propagated when patients undergo certain treatments including continuous positive airway pressure (PAP) therapy. This study aimed to assess the degree of viable virus propagated from mask leak in a PAP circuit and the mitigation of virus propagation by an air filter combined with a plastic canopy. Methods: Bacteriophage PhiX174 (108 copies/mL) was nebulised into a custom PAP circuit within a non-vented clinical room. Mask leak was systematically varied to allow 0, 7, 21, 28 and 42 L/min at the mask interface. Plates containing Escherichia coli host assessed the degree of viable virus (via plaque forming unit) settling on surfaces around the room. In order to contain virus spread, the efficacy of a simple, low-cost ventilated headboard, created from a plastic tarpaulin hood and a high efficiency particulate air (HEPA) filter was tested. Findings: Increasing mask leak was associated with virus contamination in a dose response manner (χ2 = 58.24, df=4, p<0.001). Clinically relevant levels of leak (≥21 L/min) were associated with virus counts equivalent to using PAP with a standard vented mask. The highest frequency of viruses was detected on surfaces 1m from the leak source, however, viable viruses were recorded on all plates (up to 3.86m from source). A plastic hood with HEPA filtration significantly reduced viable viruses on all plates. HEPA exchange rates of 170 and 470m3/hr eradicated all evidence of virus contamination. Interpretation: Mask leak from PAP circuits may be a major source of environmental contamination and nosocomial spread of infectious respiratory diseases. Subclinical levels of leak should be treated as an infectious risk. Cheap and low-cost patient hoods with HEPA filtration are an effective countermeasure. Funding: National Health and Medical Research Council of Australia (1139745). Declaration of Interests: GSH and DM have received equipment to support research from ResMed, Philips Respironics and Air Liquide Healthcare. BAE has received funding from Apnimed.