Prevalence, characteristics and outcomes of respiratory viral co-infection among hospitalized children

Respiratory tract infections (RTIs) are a leading cause of pediatric hospitalization. Although multiple concurrent viral infections are frequently detected, their impact on clinical outcomes remains unclear. This study evaluated whether viral co-infection in children leads to worse clinical outcomes, higher inflammatory markers, or increased medical management compared to single-virus infections. We retrospectively studied children aged 0-18 years hospitalized with RTIs at a tertiary pediatric center (2017-2024). Inclusion required at least one virus detected by multiplex polymerase chain reaction (PCR). Clinical, laboratory, and hospitalization data were compared between children with single versus multiple viral infections. Multivariable regression models adjusted for age, sex, and season were used to assess associations with clinical outcomes. Of 5,703 hospitalized children, 1,120 (19.6%) had multiple viral infections. Co-infected children were younger (median 0.9 years [IQR 0.5-1.6] vs. 1.2 [IQR 0.4-3.2], p < 0.0001) and more likely to have elevated inflammatory markers, including higher C-reactive protein (CRP) and white blood cell (WBC) counts. Despite these differences, key hospitalization outcomes, including length of stay (median 4 days [IQR 3-6] in both groups), intensive care unit (ICU) admission (8.0% vs. 7.2%), and 30-day rehospitalization rates, did not differ significantly. Co-infected patients were more frequently treated with bronchodilators and steroids. CONCLUSIONS: Viral co-infections were common, particularly among younger children, and were associated with modestly higher inflammatory responses and increased use of anti-inflammatory medications. However, co-infection did not significantly affect hospitalization duration or ICU admission. These findings suggest that multiple viral infections may not substantially worsen disease severity in hospitalized children. WHAT IS KNOWN: • Viral co-infections are common in pediatric respiratory illness, yet their impact on clinical severity and outcomes remains debated and inconsistent in current literature. WHAT IS NEW: • Co-infection is associated with significantly higher inflammatory markers and increased use of steroids and bronchodilators compared to single-virus infections. • Despite laboratory differences and higher medication use, co-infection does not increase length of stay, ICU admission rates, or 30-day rehospitalization.