Australian RSV epidemic seasonality – but not severity – altered by COVID-19

 1. RSV infections and hospitalizations peaked in December of 2020, a significant change in timing from the usual autumn and winter epidemics of the last six years, according to epidemiologic research from the Sydney Children’s Hospital Network.

2. There were significant differences in age distribution of RSV disease burden, but not disease severity, as measured by hospitalizations and pediatric ICU admissions.

Evidence Rating Level: 2 (Good)

Study Rundown: Australian epidemiologists and pediatricians noted an unseasonal spike of illness due to respiratory syncytial virus in the summer of 2020. In a retrospective multicenter analysis, the Sydney Children’s Hospital Network quantified the timing and frequency of PCR confirmed RSV illness, inpatient hospitalizations with RSV or bronchiolitis, and emergency room visits for acute respiratory infection in the year 2020. Utilizing data from January 2014-December 2019, the team modeled expected lab-confirmed RSV infection in New South Wales in 2020, stratifying by patient age and disease severity. Compared to this model, the incidence of RSV infection was found to be uncharacteristically low in the autumn and winter months of 2020, with a sharp spike peaking in mid-December. This change in timing of endemic RSV infections correlated with relaxed COVID-19 safety measures and the end of a regional school holiday. A significantly higher RSV disease burden was identified in patients 2-4 years of age when compared to the preceding six years, though no other age range was similarly affected. No significant difference in RSV disease severity – measured by proportion of hospitalization and ICU admission – was identified. Decreases in ER utilization and hospitalization for RSV and bronchiolitis were observed. Reliance on disease-specific billing codes to track hospitalizations may lead to underestimation of a population’s disease burden, a problem confounded by increased viral testing during the pandemic. However, the robust forecasting and analysis of lab-confirmed RSV infections in the context of public safety measures and changes in remote vs in-person education provide compelling evidence regarding the effects of COVID-19 mitigation strategies on the transmission patterns and diversity of previously endemic respiratory viruses.

Click to read the study in Pediatrics

Relevant Reading: Where has all the influenza gone? The impact of COVID-19 on the circulation of influenza and other respiratory viruses, Australia, March to September 2020

In-Depth [retrospective cohort]:  This retrospective cohort study collected data from January 2014-December 2019 of positive RSV laboratory testing; inpatient admissions coded as RSV, bronchiolitis due to RSV, and unspecified bronchiolitis; and ED visits coded for RSV or acute respiratory infection to create a time series analysis model estimating the expected 2020 epidemiology of RSV infections. The model was stratified by age group and estimated disease severity by proportion of hospitalizations and ICU admissions. RSV levels were significantly lower than expected in autumn and winter, increasing rapidly in December of 2020 for an off-season peak before rapidly decreasing. RSV infections in 2020 were significantly higher in the 2-4 y/o age range (% difference from expected 83.91, 95% CI 34 to 192, p<0.01), with no other age groups seen to have alteration in disease burden. Total RSV-coded hospitalizations (-32%, 95% CI -41 to -19, p<0.01) and acute respiratory infection-coded ER visits (-33%, 95% CI -46 to -12, p<0.05) decreased significantly. The proportion of RSV hospitalizations requiring ICU admission either remained static or decreased significantly based on patient age.

Image: PD

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