Respiratory Syncytial Virus Genomic Load and Disease Severity Among Children Hospitalized With Bronchiolitis: Multicenter Cohort Studies in the United States and Finland

Background. We investigated whether children with a higher respiratory syncytial virus (RSV) genomic load are at a higher risk of more-severe bronchiolitis. Methods. Two multicenter prospective cohort studies in the United States and Finland used the same protocol to enroll children aged <2 years hospitalized for bronchiolitis and collect nasopharyngeal aspirates. By using real-time polymerase chain reaction analysis, patients were classified into 3 genomic load status groups: low, intermediate, and high. Outcome measures were a length of hospital stay (LOS) of ≥3 days and intensive care use, defined as admission to the intensive care unit or use of mechanical ventilation. Results. Of 2615 enrolled children, 1764 (67%) had RSV bronchiolitis. Children with a low genomic load had a higher unadjusted risk of having a length of stay of ≥3 days (52%), compared with children with intermediate and those with high genomic loads (42% and 51%, respectively). In a multivariable model, the risk of having a length of stay of ≥3 days remained significantly higher in the groups with intermediate (odds ratio [OR], 1.43; 95% confidence interval [CI], 1.20–1.69) and high (OR, 1.58; 95% CI, 1.29–1.94) genomic loads. Similarly, children with a high genomic load had a higher risk of intensive care use (20%, compared with 15% and 16% in the groups with low and intermediate genomic loads, respectively). In a multivariable model, the risk remained significantly higher in the group with a high genomic load (OR, 1.43; 95% CI, 1.03–1.99). Conclusion. Children with a higher RSV genomic load had a higher risk for more-severe bronchiolitis.