Abstract
This cohort study examined changes in RSV age distribution and disease severity in Colorado children after the COVID-19 pandemic.
Respiratory syncytial virus (RSV) experienced a global resurgence 2 years into the COVID-19 pandemic, with record-breaking hospitalization rates in young children.1 Differences in children hospitalized with RSV during the current period (2022-2023) compared with periods prior to COVID-19 remain unclear. In this analysis, we compared age distributions and disease severity in children hospitalized with RSV in Colorado between 2018 and 2023.
Methods
For this cohort study, we analyzed public health surveillance data from the Centers for Disease Control and Prevention Emerging Infections Program (EIP) RSV Hospitalization Surveillance Network.2 Our analysis included residents of the Colorado EIP catchment area younger than 18 years and hospitalized at Children’s Hospital Colorado (primary pediatric provider for the EIP catchment area) with polymerase chain reaction (PCR)–confirmed RSV infection. The University of Colorado institutional review board deemed the study exempt from review and waived the informed consent requirement because only deidentified data were used. We followed the STROBE reporting guidelines.
We compared the age distribution of children hospitalized with RSV over 4 periods (2018-2019, 2019-2020, 2021-2022, and 2022-2023). The 2020-2021 period was excluded due to only 1 hospitalization. From October 2021, all children admitted to Children’s Hospital Colorado underwent combination SARS-CoV-2/influenza/RSV PCR testing. We compared median ages and length of hospital stay using Wilcoxon rank sum tests and proportions using χ2 tests. Significance was set at a 2-sided P < .05. Data were analyzed with SAS version 9.4 (SAS Institute).
Results
The analysis included 2809 children (mean [SD] age, 21.6 [25.6] months), with 1501 boys (53.3%) and 1307 girls (46.6%). During the 2021-2022 and 2022-2023 periods, 97.5% and 98.8% of hospitalizations, respectively, were directly related to RSV infection. Age distributions differed significantly over these periods (Figure), with a median (IQR) age of 11.0 (3.0-26.0) months prior to 2022-2023 compared with 18.5 (6.0-37.8) months in the first 6 weeks of the 2022-2023 period (P < .001). Compared with prior periods, a greater proportion of children hospitalized with RSV in 2022-2023 were aged 2 to younger than 5 years (34.2% in 2022-2023 vs 23.4% in prior periods) and aged 5 to younger than 12 years (9.7% and 5%, respectively) (both P < .001). The proportion of hospitalized children with RSV admitted to the intensive care unit was 27.1% during the 2021-2022 period and 36.0% during the 2022-2023 period (P < .001), with a median length of stay of 3.0 and 3.8 days (P < .001), respectively (Table).
Figure. Ages of Children Hospitalized Due to Respiratory Syncytial Virus (RSV) Infection .
Only one pediatric RSV-associated hospitalization occurred in 2020-2021; therefore, this period is excluded. The horizontal bar inside the boxes indicates the median and the lower and upper ends of the boxes are the IQRs. The whiskers represent minimum and maximum values. Outliers are omitted. Age distributions among the 4 periods differed significantly according to Kruskal-Wallis testing (P < .001). Hospitalizations included both observations and inpatient admissions.
Table. Comparison of Length of Hospital Stay and Intensive Care Unit (ICU) Admission Among Pediatric Hospitalizations Associated With Respiratory Syncytial Virus (RSV) in Colorado During the 2021-2022 and 2022-2023 Periods.
| 2021-2022 (n = 748) | 2022-2023 (n = 637)a | P value | |
|---|---|---|---|
| Hospital length of stay, median (IQR), d | 3.0 (2.0-4.5) | 3.8 (2.7-5.5) | <.001 |
| ICU admission, No. (%) | 203 (27.1%) | 229 (36.0%) | <.001 |
| Age distribution among children admitted to the ICU, %b | |||
| 0-5 mo | 35.3 | 41.7 | <.001 |
| 6-11 mo | 33.6 | 33.7 | |
| 12-23 mo | 20.7 | 43.0 | |
| 24 mo-4 y | 21.1 | 31.1 | |
| 5-11 y | 10.3 | 28.3 | |
| 12-17 y | 16.7 | 0 |
Data from the 2022-2023 period are from October 1 to November 15, 2022.
Percentages indicate the proportion of hospitalized children in a given age group with positive RSV test results who were admitted to the ICU.
Discussion
These findings support the hypothesis that lack of previous exposure to RSV during the COVID-19 pandemic may be associated with the current surge in RSV infections among an older cohort of susceptible children.3,4 This surge may be associated with pandemic mitigation measures, which can limit the transmission of respiratory viruses. Similarly, the data suggest that waning immunity in children and pregnant mothers without repeated exposure to RSV may contribute to more severe disease in infants and older children compared with previous periods.5 It is also possible that the RSV strain in the 2022-2023 period was more virulent or that immune dysregulation from prior SARS-CoV-2 infection was associated with increased susceptibility to subsequent RSV infections.6
Study limitations include use of data from a single region and variation in testing practices during the study, since universal RSV testing among hospitalized children was adopted in October 2021. However, we do not anticipate that adoption of a different testing tool affected detection rates, given the high sensitivity of PCR in symptomatic patients; furthermore, during the period of universal testing, most children (>97%) were admitted due to RSV symptoms, rather than having an incidental positive test result. Additionally, any efforts to decrease testing prior to the pandemic would have affected testing in all age groups.
Multisite studies are needed to corroborate these findings. These data may help inform the introduction of imminent new RSV prevention strategies, including vaccines and monoclonal antibodies, to minimize disease burden in this age group.
Data Sharing Statement
References
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Associated Data
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Supplementary Materials
Data Sharing Statement
