Impact of Respiratory Syncytial Virus Subtype and Viral Load on the Clinical Course and Disease Severity of Acute Respiratory Tract Infection in Hospitalized Children

Background: Respiratory syncytial virus (RSV) is a leading cause of hospitalization in children. The impact of viral factors like RSV subtype and viral load (VL) on disease severity remains unclear. Methods: We screened 1171 hospitalized children ≤3 years of age with respiratory symptoms in winter seasons (2017–2020) for RSV infection by Reverse Transcription Polymerase Chain reaction. Disease severity was assessed using length of hospital stay and a previously validated disease severity score (RSV-CLASS, range 0–4, higher scores indicating more severe disease). Univariate/multivariate analyses were performed to identify predictors of VL. Results: In total, n = 351/1171 children were tested RSV positive (RSV A: n = 146/351 41.6%, RSV B: n = 205/351 58.4%) with a median VL of 4.7 × 10 8 (interquartile range IQR 5.6 × 10 7 to 1.3 × 10 9 ). The median age was 3.5 months (IQR 1.5–11.0), and most children were <6 months (n = 223/351 63.5%). Bronchiolitis was the leading admission diagnosis, and children were hospitalized for a median duration of 3 days (IQR 2–5), and the median RSV-CLASS disease severity score value was 2 (IQR 1–3). Higher clinical severity scores were observed in children with lower respiratory tract infections ( P < 0.01) and were associated with longer hospital stay (ρ = 0.14, 95% confidence interval CI: 0.04–0.25). Clinical symptoms did not differ between RSV subtypes. However, younger age, shorter symptom duration, lower weight and reduced blood leukocyte count were associated with higher VL. In multivariate linear regression analysis adjusted for age and sex, weight and leukocyte count remained significant. Conclusions: This study highlights that RSV subtype and VL are not associated with disease severity in hospitalized children.