Respiratory syncytial virus genomic load and disease severity among children hospitalized with bronchiolitis: multicenter cohort studies in the United States and Finland

Abstract

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.

Keywords: bronchiolitis; children; cohort study; genomic load; hospitalization; infants; intensive care unit; length of stay; mechanical ventilation; respiratory syncytial virus.

Figure 1.

Unadjusted association of respiratory syncytial virus genomic load with the risk of a length of hospital stay (LOS) of ≥3 days in children hospitalized for bronchiolitis. The fitted line represents locally weighted scatterplot smoothed (lowess) curve. Lower threshold cycle (CT) values indicate higher RSV genomic loads. There was a positive relationship between RSV genomic load (an inverse of the CT value) and the risk of a LOS of ≥3 days (P < .001).