Respiratory Viral Detection in Children Pre- and Post-COVID-19

Source: Teoh Z, Toepfer AP, Rohlfs C, et al. Viral detection in children <5 years with bronchiolitis, pneumonia, and croup, new vaccine surveillance network, 2017–2023. J Pediatric Infect Dis Soc. 2025;14(11):piaf096; doi: 10.1093/jpids/piaf096.Investigators from multiple institutions conducted a retrospective study to assess the association between respiratory viruses and specific acute respiratory illnesses, including bronchiolitis, pneumonia, and croup in children <5 years old, and evaluate changes in the viruses associated with these ARI prior to, and following, the COVID pandemic. For the study, they reviewed data in the New Vaccine Surveillance Network (NSVN). As part of the NSVN, respiratory tract samples are collected for clinical care or for research purposes and assayed for multiple respiratory viruses in children with 1 or more symptoms of ARI at 7 medical centers in the US. Participants in the current study were patients <5 years old, with an inpatient admission or ED visit at 1 of the NSVN centers between 2017 and 2023 who had an ICD-10 code consistent with a diagnosis of bronchiolitis, pneumonia, or croup. Data collected on these participants included specific diagnoses, age, respiratory virus assay results, and date of encounter. The proportion of children with each of the ARI conditions of interest in whom a respiratory virus was detected was determined, and frequency of each virus detected in patients with bronchiolitis, pneumonia, and croup calculated. Chi-square tests were used to compare changes in proportions of different viruses associated with each of the ARI syndromes during the prepandemic (2017–2019) and post-pandemic (2021–2023) periods.Data were analyzed on 19,447 children, including 14,340 diagnosed with bronchiolitis, 4,423 with pneumonia, 2,367 with croup, 1,541 with bronchiolitis and pneumonia, 107 with bronchiolitis and croup, and 42 with pneumonia and croup. The median age of participants with bronchiolitis, pneumonia and croup was 8 months, 23 months and 18 months, respectively. At least 1 respiratory virus was detected in 89% cases of bronchiolitis, 81% of those with pneumonia, and 82% of patients with croup. Respiratory syncytial virus (RSV) was the most commonly detected virus associated with bronchiolitis (41% of cases) and pneumonia (26%). The most commonly detected virus in patients with croup was parainfluenza virus (28%). Rhinoviruses/enteroviruses (RV/EV) were the second most commonly detected virus in cases of bronchiolitis (18.9%), pneumonia (18.0%), and croup (14.4%). The proportion of viruses detected in children with bronchiolitis and pneumonia was relatively similar in the pre- and post-pandemic periods. However, the proportion of patients with croup associated with parainfluenza decreased from 33.8% in the prepandemic period to 25.4% post-pandemic (P <0.001). Detection of influenza decreased significantly from pre- to post-pandemic in all 3 ARI conditions. During the post-pandemic period, the proportion of cases of bronchiolitis, pneumonia, and croup in which SARS-CoV-2 was detected was 1%, 1.5%, and 7.6%, respectively.The authors conclude that a respiratory virus was detected in a high proportion of children <5 years old with bronchiolitis, pneumonia, and croup.Dr Chan has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Bronchiolitis, pneumonia, and croup are among the most common causes of respiratory-related infections and hospitalizations in pediatrics.1 Typically, RSV, influenza, and parainfluenza respiratory infections occur in predictable patterns, but the COVID-19 pandemic disrupted the seasonality of respiratory viral infections.2 Multi-center studies investigating the seasonality of respiratory infections post-COVID-19 have been limited.3The authors of the current study performed a multicenter study to characterize viral detection and clinical presentation in children under 5 years old who presented with bronchiolitis, pneumonia, or croup between 2017–2023. The study included more than 21,000 children and found that >80% had at least 1 respiratory virus detected, most commonly RSV, RV/EV, and PIV. Most viruses were detected in similar proportions pre- and post-covid emergence except for PIV, which was decreased in croup cases post-COVID-19 onset. This was hypothesized to be due to the proportional increased detection of SARS-CoV-2 in the same timeframe.Strengths of the study include its geographically diverse cohort, large number of cases, and multi-year investigation, which allowed for a cohesive comparison over time. Limitations include the concerns that study sites may not be entirely representative of the nation, reliance on coding for diagnosis, variability in diagnostic testing practices, and limited ability to correlate viral detection with clinical presentation.In children under 5 years old presenting with bronchiolitis, pneumonia, or croup, there is a high likelihood of identifying at least 1 viral pathogen.