Respiratory syncytial virus activity--United States, July 2011-January 2013.

Respiratory syncytial virus (RSV) causes lower respiratory infections among infants and young children worldwide. During 1997-2006, an estimated 132,000-172,000 children aged <5 years were hospitalized for RSV infection annually in the United States. In temperate climate zones, RSV generally circulates during the fall, winter, and spring, but the exact timing and duration of RSV seasons vary by region and year. To determine seasonal trends in the circulation of RSV at national and regional levels, data collected by the National Respiratory and Enteric Virus Surveillance System (NREVSS) were analyzed. For 2011-12, the RSV season onset ranged from late October to mid-January and season offset ranged from early March to early May in all 10 U.S. Department of Health and Human Services (HHS) regions, excluding Florida. Florida is reported separately because it has an earlier season onset and longer duration than the rest of the country. For data reported as of January 7, 2013, RSV onset for the 2012-13 season occurred in all but one of the HHS regions by December 15, 2012. Seasonal patterns remained consistent with previous years and demonstrated the usual differences in RSV circulation among HHS regions. Health-care providers and public health officials can use information on RSV circulation to guide diagnostic testing and timing of RSV immunoprophylaxis for children at high risk for severe respiratory infection.