Respiratory syncytial virus load, viral dynamics, and disease severity in previously healthy naturally infected children.

BACKGROUND: Respiratory syncytial virus (RSV) disease severity was thought to be a result of host immunopathology but alternatively may be driven by high-level viral replication. The relationships between RSV load, viral clearance dynamics, and disease severity have not been carefully evaluated. METHODS: Previously healthy RSV-infected children <2 years old were recruited. RSV load was measured in respiratory secretions by fresh quantitative culture over 3 hospital days. Measures of disease severity were hospital admission, duration of hospitalization, requirement for intensive care, and respiratory failure. RESULTS: Multivariate logistic regression models revealed independent predictors of increased duration of hospitalization: male sex, lower weight, and higher viral load on any day. Viral loads at day 3 were more significantly associated with requirement for intensive care and respiratory failure than were viral loads at earlier time points. Faster RSV clearance was independently associated with shorter hospitalization. DISCUSSION: These observations challenge the immunopathology-based pathogenesis paradigm. They also have major therapeutic implications, suggesting that application of antiviral agents early in the disease course, even at a time when viral replication is at its highest, might improve subsequent morbidity by significantly lowering viral load and direct viral cytopathic effects, and aborting the potential downstream immunopathology.