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Brief Report: Respiratory Syncytial Virus Activity --- United States, 2004--2005

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections (LRTIs) (e.g., bronchiolitis and pneumonia) among young children, resulting in an estimated 51,000--82,000 hospitalizations annually in the United States (1). RSV also causes severe disease and death among older persons (2,3) and persons of all ages with compromised respiratory, cardiac, or immune systems and can exacerbate chronic cardiac and pulmonary conditions (4,5). In temperate climates, most RSV infections occur during a distinct seasonal peak. This report presents preliminary data from RSV activity reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS) for the weeks ending July 2 through December 3, 2005, indicating the onset of the 2005--06 RSV season, and summarizes trends during July 2004--June 2005. 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 (6), and provide appropriate immune prophylaxis to eligible children, including certain premature infants or infants and children with chronic lung and heart disease (7).

NREVSS is a voluntary, laboratory-based surveillance system of 89 clinical and public health laboratories in 38 states and the District of Columbia.* Laboratories report weekly to CDC the number of specimens tested and the number positive for certain respiratory and enteric viruses. During July 2004--June 2005, of 135,491 tests for RSV reported, 19,642 (14.5%) were positive. Widespread RSV activity began the week ending November 13, 2004, and continued for 21 weeks until April 2, 2005. Activity appeared highest during December for the South and Northeast, during January for the West, and during February for the Midwest (Figure). Regionally, RSV activity occurred first in the South (37 sites reporting activity; median weeks of onset and conclusion: November 2, 2004, and February 26, 2005, respectively), later in the Northeast (nine sites; November 20, 2004, and March 8, 2005) and West (19 sites; December 18, 2004, and March 26, 2005), and last in the Midwest (20 sites; January 1, 2004, and April 12, 2005). Although 94% of RSV detections were reported during the weeks ending November 13, 2004--April 2, 2005, sporadic detections were reported throughout the year. During May--October 2005, laboratories in 23 states reported RSV detections.

For the current reporting period (July 2--December 3, 2005), 84 laboratories in 38 states reported testing for RSV. Since October, 62 participating laboratories have reported RSV detections. Preliminary 2005--06 data suggest that the annual seasonal peak began in the South during the week ending October 15 (Figure).

Health-care providers should consider RSV as a potential cause of acute respiratory disease among persons in all age groups during the annual seasonal peak. RSV infection is the most common cause of hospitalization for acute respiratory disease among children aged <12 months (8). RSV infection also is increasingly recognized as a cause of hospitalization among older adults (2). Laboratory testing of nasal secretions for virus or viral antigen (e.g., immunofluorescence or enzyme-linked immunosorbent assays) can be sensitive for diagnosis in infants and children aged <5 years but is less sensitive for diagnosis in older children and adults. Testing nasal secretions for viral RNA by well-designed reverse transcription-polymerase chain reaction assays can be sufficiently sensitive to detect most RSV infections in all age groups (9).

No vaccine is currently available for RSV. However, infection control measures are important for preventing transmission in health-care settings (6). Infants and children at risk for serious RSV infection can receive immune prophylaxis with monthly doses of a humanized murine anti-RSV monoclonal antibody product during the RSV season (7). Infants and children at risk include 1) those aged <24 months with chronic lung disease who have required medical therapy (e.g., supplemental oxygen, bronchodilator, diuretic, or corticosteroid therapy) within 6 months of RSV season onset, 2) those with hemodynamically significant heart disease, and 3) preterm infants born at <32 weeks' gestation or preterm infants born at 32--35 weeks' gestation with at least two additional risk factors (e.g., day care attendance, exposure to environmental pollutants, school-aged siblings, congenital abnormality of the airways, or neuromuscular disease) during their first RSV season.

Because onset of RSV activity can vary among regions and communities, physicians and health-care facilities should consult their local clinical laboratories for the latest data on RSV activity (10). Additional information and updates on national and regional RSV trends are available at

Reported by: National Respiratory and Enteric Virus Surveillance System collaborating laboratories. KJ Felton, AM Fry, MD, LJ Anderson, MD, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.


  1. Shay DK, Holman RC, Newman RD, Liu LL, Stout JW, Anderson LJ. Bronchiolitis-associated hospitalizations among U.S. children, 1980--1996. JAMA 1999;282:1440--6.
  2. Falsey AR, Hennessey PA, Formica MA, Cox C, Walsh EE. Respiratory syncytial virus infection in elderly and high-risk adults. N Engl J Med 2005;352:1749--59.
  3. Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 2003;289:179--86.
  4. Welliver RC. Review of epidemiology and clinical risk factors for severe respiratory syncytial virus (RSV) infection. J Pediatr 2003;143 (5 Suppl):S112--7.
  5. Falsey AR, Walsh EE. Respiratory syncytial virus infection in adults. Clin Microbiol Rev 2000;13:371--84.
  6. CDC. Guidelines for preventing health-care--associated pneumonia, 2003: recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee. MMWR 2004;53(No. RR-3).
  7. Meissner HC, Long SS; American Academy of Pediatrics Committee on Infectious Diseases and Committee on Fetus and Newborn. Revised indications for the use of palivizumab and respiratory syncytial virus immune globulin intravenous for the prevention of respiratory syncytial virus infections. Pediatrics 2003;112:1447--52.
  8. Iwane MK, Edwards KM, Szilagyi PG, et al. Population-based surveillance for hospitalizations associated with respiratory syncytial virus, influenza virus, and parainfluenza viruses among young children. Pediatrics 2004;113:1758--64.
  9. Falsey AR, Formica MA, Treanor JJ, Walsh EE. Comparison of quantitative reverse transcription-PCR to viral culture for assessment of respiratory syncytial virus shedding. J Clin Microbiol 2003;41:4160--5.
  10. Mullins JA, Lamonte AC, Bresee JS, Anderson LJ. Substantial variability in community respiratory syncytial virus season timing. Pediatr Infect Dis J 2003;22:857--62.

* Northeast: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont; Midwest: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin; South: Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia; West: Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.

Widespread RSV activity is defined by NREVSS as the first of 2 consecutive weeks when 50% of participating laboratories report RSV detections or isolations and when the mean percentage of specimens positive by antigen detection is >10%.


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Date last reviewed: 12/15/2005


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