Background: Respiratory syncytial virus (RSV), a leading viral respiratory pathogen worldwide, has 2 major subtypes, A and B.
Objective: To describe the temporal and geographic distribution and parameters of disease severity associated with RSV A and B in the United States.
Methods: A US multicenter active surveillance study was conducted in emergency departments (EDs) during 2 RSV seasons. Infants <1 year of age presenting to the ED with symptoms of lower respiratory tract infection or apnea were enrolled. RSV subtypes were detected in nasal swabs by reverse transcriptase polymerase chain reaction.
Results: Of 4248 patients enrolled, 4172 patients were evaluable; 32.4% of patients were positive for any RSV subtype in season 1 and 29.9% in season 2. RSV A and B were detected in each region studied. More patients presented to the ED with RSV A than with RSV B (853 [20.4%] versus 453 [10.9%], respectively); RSV A–positive patients were more likely to be admitted to the hospital or intensive care unit (47.7%, versus RSV B, 35.8%; P < 0.0001); hospitalized RSV A–positive patients were less likely to be prescribed antibiotics (32.4%, versus RSV B, 47.8%; P < 0.001).
Conclusions: This is the largest epidemiologic study in EDs reporting trends in RSV subtypes. RSV subtypes A and B were documented in both seasons across all US regions studied and detected in September to May. The results of this study support suggestions from smaller studies that RSV A may be more virulent than RSV B; however, more quantitative assessments of disease severity are needed.