Following the onset of the COVID-19 pandemic, RSV infections deviated from a previously reliable epidemiologic pattern of presentation. To investigate whether this change in RSV seasonality resulted in a change in frequency and severity of RSV infections, this single center retrospective study compares demographic and hospital factors during RSV seasons before and after the onset of the COVID-19 pandemic.

Included were patients under age 5 years who tested positive for RSV only by RT-PCR in our pediatric emergency departments during the last three RSV seasons before the onset of the COVID-19 pandemic in spring 2020, as compared to the first three seasons after the pandemic started. RSV seasonality was defined as periods in which greater than 10 % of all RSV RT-PCR tests sent resulted positive. Patients with tracheostomies were excluded, as were duplicate tests performed in the same patient within 1 day. Demographic data obtained included patient age, sex, and weight. Hospital factors obtained were inpatient admission and length of stay (LOS), intensive care unit (ICU) admission and LOS, respiratory support during the encounter, and mortality. A planned subgroup analysis isolating the first RSV season after the pandemic's onset was performed. Mann-Whitney and Pearson Chi-Square testing were used for comparison of continuous and categorical variables, respectively. Significance was set at p < 0.05.

RSV seasons were identified with 7592 cases meeting study criteria (2770 cases before the pandemic's onset and 4822 cases after). While there were more RSV cases identified per season after the onset of COVID-19, testing also increased in this period. RSV positive patients in seasons after the onset of COVID-19 were significantly older than those in seasons before (0.83 years vs. 0.56 years, p < 0.001). They were admitted to the hospital significantly less (46.8 % vs. 54.9 %, p < 0.001), though ICU admission rates did not change significantly (32.9 % vs. 31.1 %, p = 0.25). Both inpatient LOS (64 h vs. 60 h, p = 0.01) and ICU LOS (68 h vs. 88.5 h, p < 0.001) decreased significantly. RSV positive inpatients in seasons after the onset of COVID-19 were significantly more likely to require respiratory support (89.0 % vs. 86.5 %, p = 0.02), with more requiring BIPAP (11.3 % vs. 8.1 %, p = 0.003) and fewer requiring intubation (9.6 % vs. 13.8 %, p < 0.001).

During the first three RSV seasons after the onset of the COVID-19 pandemic, our pediatric emergency departments saw more RSV positive patients than in the last three seasons beforehand. These patients were significantly older and less likely to be admitted, which may be partly due to increased respiratory viral testing during the pandemic. However, shorter LOS and decreased intubations despite increased respiratory support among admitted patients may indicate a paradigm shift in emergency department and inpatient management of severe RSV infections, perhaps encouraged by practice changes and resource limitations due to COVID-19. This information may better guide institutions in predicting resource needs after large-scale infectious disease outbreaks in the future.