Viral Detection in Children <5 Years with Bronchiolitis, Pneumonia, and Croup, New Vaccine Surveillance Network, 2017-2023

Abstract Introduction Bronchiolitis, pneumonia, and croup account for a substantial burden of pediatric hospitalizations. We aim to provide an updated, multi-center, multi-pathogen evaluation of viral detections seen with these acute respiratory illness (ARI) syndromes before and after the COVID-19 pandemic. Methods We included children <5 years with a diagnosis of bronchiolitis, pneumonia, or croup during 2017-2023 from the New Vaccine Surveillance Network. Respiratory viruses were detected with a research ± clinical respiratory swabs; demographic and clinical data were obtained from caregiver interview and chart review. Virus-specific proportions across all three ARI syndromes were described, including comparisons stratified by age, surveillance year including pre- (2017-2019) and post (2021-2023) COVID-19 onset periods, and underlying medical condition. Results Among 14 340 cases of bronchiolitis, 4423 cases of pneumonia, and 2367 cases of croup, >80% had one or more respiratory virus detected. Respiratory syncytial virus (RSV) was the most frequent virus detected in bronchiolitis (41%) and pneumonia (26%), with a similar distribution across the COVID-19 onset periods. Parainfluenza virus (PIV) was the most frequent virus detected in croup (28%), but detections fell in the post-COVID-19 onset period by 8.4%; there was a comparable proportion of SARS-CoV-2 detections (7.6%) that emerged among croup cases. Rhinoviruses/enteroviruses (RV/EV) were the second most frequently detected virus across all three ARI syndromes and were the predominant virus in children <6 months and children with an underlying medical condition diagnosed with croup. Codetections were present in 17%-19% of bronchiolitis, pneumonia, and croup cases. Discussion We found a high proportion of respiratory viral detections in children <5 years with bronchiolitis, pneumonia, or croup, particularly with RSV, RV/EV, and PIV. Most viruses were identified in similar proportions before and after the emergence of SARS-CoV-2, except for PIV and influenza virus. In our cohort, there was a high proportion of viral detection across all three ARI syndromes, with RV/EV frequently detected in certain age groups and among children with underlying conditions.