Respiratory Syncytial Virus --- United States, July 2007--June
2011 Each year in the United States, an estimated 75,000--
125,000 hospitalizations related to respiratory syncytial virus
(RSV)occur among children aged <1 year, and RSV infection
results in approximately 1.5 million outpatient visits among
children aged <5 years (1,2). In the United States, RSV season
begins in the fall, peaks in winter, and ends in the late winter
and early spring (3). However, the exact timing and duration
vary from year to year and by geographic region (4). To describe
trends in RSV seasonality, data from the National Respiratory
and Enteric Virus Surveillance System (NREVSS) were used to
determine the onset, offset, and peak of the July 2010--June
2011 RSV season, and for an aggregate analysis of the four most
recent RSV seasons (July 2007--June 2011). During 2010--11,
excluding Florida, season onset occurred from mid-November to
early January, and offset occurred from mid-March to late April
across all 10 U.S. Department of