Epidemiology of respiratory syncytial virus in Central Queensland, Australia.

Abstract: Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in infants. Little is known about the epidemiology, burden, and seasonality of RSV in subtropical regions of Australia like Central Queensland. This information is important to plan prevention strategies, including therapeutics, future vaccines, and health system preparedness. We collected data on laboratory-confirmed RSV cases and admissions in Central Queensland for the period 1 July 2021 to 31 December 2022. From July 2021, RSV was listed as a nationally notifiable condition on laboratory-confirmed diagnosis. During the study period, 1,142 laboratory-confirmed cases of RSV (50.0% female sex) were reported, with 169 cases (14.8%) requiring hospital admission, 12 of which (7.1%) required intensive care unit/high dependency unit admissions; two deaths occurred. Of cases requiring hospital admission, RSV was listed as the primary diagnosis in 113/169 cases (66.9%); 63/169 admitted cases (37.3%) had a major comorbidity. Of all cases, 55.4% were in children < 5 years of age (20.9% hospitalised); 35.7% in children < 2 years of age (24.3% hospitalised), and 19.1% in children < 12 months of age (27.5% hospitalised). Children under five years of age made up 78.1% of admissions, a rate of 9.0 admissions per 1,000 children over the 18-month study period, with an average age of 15.8 months (standard deviation, SD: 13.1 months) in this cohort. Indigenous children aged < 5 years were over-represented in cases (rate ratio, RR: 1.6; 95% confidence interval [95% CI]: 1.3-1.9) and admissions (RR: 1.6; 95% CI: 1.0-2.4). Antibiotics were prescribed to 48.5% of admitted cases under two years of age, despite documented bacterial infection in only 26.3% of these cases; antibiotic prescription was significantly higher in those who received a chest X-ray (p < 0.001). Of all cases, 33.5% occurred in July 2022 alone, with greater than 75.0% of cases occurring during June-August 2022. RSV showed year-round activity with a distinctive winter peak in 2022; however, this season was likely affected by coronavirus disease 2019 (COVID-19) restrictions and behaviours. Ongoing surveillance is required to better understand the epidemiology and seasonality of RSV in Central Queensland.