Prevention of SARS-CoV-2 (COVID-19) transmission in residential aged care using ultraviolet light (PETRA): a parallel crossover randomised controlled trial

Our aim is to evaluate the respiratory viral epidemiology in residential aged care facility (RACF) environments and determine the potential of readily translatable measures to address airborne components of transmission within these settings. The study is a 4-period parallel cross-over randomised controlled trial targeting air-sterilisation strategies to reduce the burden of airborne viral infections in residential aged care settings. The intervention will use commercially available upper-room germicidal ultraviolet (GUV). Commercially available upper-room GUV (with effective air-mixing) has been shown to reduce airborne tuberculosis transmission at a rate equivalent to adding significant room air changes per hour, and its high efficacy against airborne viruses (including influenza and SARS-CoV-1) has been demonstrated. Moreover, when GUV has been deployed in "in-duct" or standalone systems, it has been shown to result in significant reductions in both viral viability and rates of symptomatic respiratory infections. These GUV modalities might therefore be combined to achieve effective air disinfection in accordance with aged care facility layout, occupancy, and air-ventilation systems. Each residential aged care facility will have the option to receive all forms of GUV intervention, with final layouts and suitability to retrospectively install determined by facility and GUV engineers. The intervention approach may use a combination of: 1. in-duct GUV placed prior to air return vents in systems serving shared spaces (such as dining areas); 2. ceiling/wall-mounted GUV units situated in a pattern that provides air sterilisation of connecting corridors and spaces between resident rooms, with additional units providing coverage to high traffic spaces (such as lift areas); and 3. standalone fan-driven GUV units used in occasional areas (such as cinema units, chapels, and workshop rooms). In situ appliance performance will be tested according to ASHRAE Standard 185.1, and deployed in such a way as to achieve an equivalent level of coverage between comparator sites. Each facility contains zones assigned to both the intervention and the control condition twice (once for each condition in each of two consecutive respiratory infection seasons). The intervention will include a treatment and a control arm: • Arm 1 (treatment): The GUV intervention will be applied for a 6-week period, followed by a 2-week washout period (to account for respiratory virus incubation periods), and then a crossover to the control period for 6-weeks, followed by a final 2-week washout. • Arm 2 (control): The control period will be applied for 6-weeks, followed by a 2-week washout period, and then a crossover to the GUV intervention will apply for 6-weeks, followed by a final 2-week washout. For each arm, the residential aged care facility engineers will be responsible for operating and modifying the GUV devices. The engineers will not be involved in the data capture or analysis process. To account for differences in facility characteristics, assessment will be based on within-facility comparisons of discrete zones, using the crossover design. Paired zones will be highly similar in size, layout, and occupancy, allowing randomisation for the control/intervention order within the study design. Similar GUV strategies will be employed in paired areas within each facility to account for temporal variation in seasonal virus levels.