Epidemiology of respiratory syncytial virus within a New South Wales-based multi-centre health district between 2018 and 2024 in Australia

Respiratory syncytial virus (RSV) epidemiology in Australia is unclear given recent advances in diagnostic testing, COVID-19 interventions, and under-recognition in older adults. Data are needed to inform new RSV vaccine use. We analysed laboratory data from all viral respiratory reverse transcription quantitative polymerase chain reaction (RT-qPCR) diagnostic tests conducted at New South Wales (NSW) Health Pathology in the South Eastern Sydney and Illawarra Health Service from 2018 to 2024. Panel and descriptive analyses were used to report annual RSV testing and detection by age group, care setting, and co-infection with other respiratory viruses using Stata v.18. Of 370,126 unique episodes tested for RSV, there were 13,293 (3.6%) detections. Public health measures for COVID-19 significantly impacted RSV circulation in 2020, with detections nearly absent in the winter season (June-August) and an off-season epidemic occurring in the summer. Annual testing and detection peaked in 2022 and was considerably higher than in pre-pandemic years (testing 6.3-fold and detection 3.4-fold higher than in 2019, respectively). Across the study period, incidence was highest in children aged <5 years (1,613 per 100,000 population). Among older adults (≥60 years of age), prevalence was 125 per 100,000. Testing was primarily performed in outpatients (71%), of which emergency departments were the most frequent care setting (49%). Of all detections, 2,713 (20.4%) had co-infections, with the most commonly co-detected viruses being rhinovirus (37%) and bocavirus (17%). RSV testing increased from 2022 due to expanded respiratory screening, RSV becoming a notifiable disease, and COVID-19 epidemics. Multiplex RT-qPCR testing increased RSV detection, but testing bias exists, with children tested more than adults. Continued surveillance across age groups is essential to assess the impact of new immunisation strategies.