Characteristics of In- and Off-season Respiratory Syncytial Virus Episodes—United States, 2016–2020

In temperate climates, respiratory syncytial virus (RSV) can occur outside the typical fall/winter/spring season. Using the Premier Healthcare Database, we identified and described hospital-based RSV episodes in the US prior to the COVID-19 pandemic (2017-2020), comparing narrowly-defined in-season (December-February) and off-season (June-August) episodes. We identified 141 427 in-season and 3756 off-season episodes among children (<18 years) and 41 735 in-season and 1243 off-season episodes among adults. Among pediatric episodes, most in- and off-season (60%, 59%) were infants. Black and Hispanic pediatric patients were over-represented in off- versus in-season episodes (Black: 22% vs 15%; Hispanic 30% vs 19%; P < .0001). Trends were similar for adults. A higher proportion of off-season pediatric episodes included antibiotics (54% vs 45%; P < .0001), and among infants and children 1-4 years, were more likely to be individuals with congenital or chronic conditions (P < .0001). Disparities due to race, ethnicity, and underlying conditions were identified among off-season cases.