Respiratory Syncytial Virus Activity — United States, 2003–2004

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections (LRTIs) (i.e., bronchiolitis and pneumonia) among young children, resulting in an estimated 51,000-82,000 hospitalizations annually. RSV causes severe disease among older adults and persons of all ages with compromised respiratory, cardiac, or immune systems, and can exacerbate chronic cardiac and pulmonary conditions. In temperate climates, RSV infections occur primarily during annual winter season outbreaks. This report summarizes trends in RSV activity reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS) during July 2003-June 2004 and presents preliminary data from the weeks ending July 3-December 4, 2004, indicating the onset of the 2004-05 RSV season. Health-care providers should consider RSV in the differential diagnosis for persons of all ages with LRTIs, implement appropriate isolation precautions to prevent nosocomial transmission, and provide appropriate immune prophylaxis to eligible children, including certain premature infants or children and infants with chronic lung and heart disease.