Background. Surveillance in 2020–2021 showed that seasonal respiratory illnesses were below levels seen during prior seasons,with the exception of interseasonal respiratory syncytial virus (RSV).

Methods. Electronic health record data of infants aged,1 year visiting the Duke University Health System from 4 October2015 to 28 March 2020 (pre–COVID-19) and 29 March 2020 to 30 October 2021 (COVID-19) were assessed. International Classification of Diseases-Tenth Revision (ICD-10) codes for RSV (B97.4, J12.1, J20.5, J21.0) and bronchiolitis (RSV codes plusJ21.8, J21.9) were used to detail encounters in the inpatient (IP), emergency department (ED), outpatient (OP), urgent care (UC), and telemedicine (TM) settings.

Results. Pre–COVID-19, 88% of RSV and 92% of bronchiolitis encounters were seen in ambulatory settings. During COVID-19, 94% and 93%, respectively, occurred in ambulatory settings. Pre–COVID-19, the highest RSV proportion was observed inDecember–January (up to 38% in ED), while the peaks during COVID-19 were seen in July–September (up to 41% in ED) across all settings. RSV laboratory testing among RSV encounters was low during pre–COVID-19 (IP, 51%; ED, 51%; OP, 41%; UC, 84%) and COVID-19 outside of UC (IP, 33%; ED, 47%; OP, 47%; UC, 87%). Full-term, otherwise healthy infants comprised most RSV encounters (pre–COVID-19, up to 57% in OP; COVID-19, up to 82% in TM).

Conclusions. With the interruption of historical RSV epidemiologic trends and the emergence of interseasonal disease duringCOVID-19, continued monitoring of RSV is warranted across all settings as the changing RSV epidemiology could affect thedistribution of health care resources and public health policy.