Brief report: respiratory syncytial virus activity--United States, July 2006-November 2007.

Respiratory syncytial virus (RSV), the most common cause of severe lower respiratory tract disease among infants and young children, typically infects persons by age 2 years and can cause subsequent infections throughout life. RSV infection primarily manifests as bronchiolitis or pneumonia and results in approximately 75,000 to 125,000 hospitalizations in the United States each year. Persons at increased risk for severe disease or death include premature infants, older adults, and persons of any age with compromised respiratory, cardiac, or immune systems. RSV is transmitted from person to person via close contact, droplets, or fomites. In temperate climates, peak RSV activity typically occurs during the winter. However, year-to-year national and regional variability in the RSV season onset and offset occurs in the United States. RSV circulation also varies by geographic location; for example, Florida has an earlier season onset and a longer season than the rest of the United States. Using data reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS), this report summarizes RSV temporal and geographic trends in the United States during the weeks ending July 8, 2006-June 30, 2007, and for the first 5 months of the current reporting season (the weeks ending July 7-November 24, 2007). Appropriately timed diagnostic tests can provide data that indicate when the RSV season begins nationally and regionally, information that has been critical in determining when to begin RSV prophylaxis for infants and children at high risk for infection.