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Brief Report: 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 (1). 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 (1--4). 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 (5), and provide appropriate immune prophylaxis to eligible children, including certain premature infants or children and infants with chronic lung and heart disease (6).

NREVSS is a voluntary, laboratory-based surveillance system of 87 clinical and public health laboratories in 40 states and the District of Columbia. The laboratories report weekly to CDC the number of specimens tested and number positive for several respiratory and enteric viruses by antigen detection and virus isolation methods. During July 2003--June 2004, of 172,247 tests for RSV reported, 21,236 (12%) were positive.

Widespread RSV activity* began the week ending November 1, 2003, and continued for 22 weeks until April 3, 2004. Activity peaked during February for all regions (Figure). Regional RSV activity occurred earliest in the South (35 sites reporting; median weeks of onset and conclusion: November 1, 2003, and March 27, 2004, respectively), later in the Northeast (seven sites; December 6, 2003, and March 27, 2004) and the Midwest (20 sites; December 6, 2003, and March 27, 2004), and latest in the West (16 sites; December 27, 2003, and April 3, 2004).

Although 93% of RSV detections were reported from the weeks ending November 1, 2003--April 3, 2004, sporadic detections were reported throughout the year. During May--October 2004, laboratories in 33 states with at least one laboratory per region reported RSV detections.

For the current reporting period (July 3--December 4, 2004), 84 laboratories in 42 states reported testing for RSV. Since November 6, a total of 50 participating laboratories have reported RSV detections. Preliminary 2004--05 data suggest that the annual outbreak has begun in two regions---in the South during the week ending October 30 and in the Northeast during the week ending November 27 (Figure).

Because RSV infection only confers partial protection from subsequent infection, reinfections occur throughout life (3,4). As a result, health-care providers should consider RSV as a cause of acute respiratory disease in all age groups during community outbreaks, particularly in young children. Rapid diagnostic techniques for clinical use vary in sensitivity and specificity. Certain assays are sensitive for diagnosis in infants and young children, but few are sensitive for diagnosis in older children and adults. Polymerase chain reaction--based assays with enhanced product detection systems can be sufficiently sensitive to detect most infections in all age groups (7,8). Accurate diagnosis of RSV infection is crucial for appropriate infection control, to rule out cocirculating viruses (e.g., influenza viruses) and to avoid inappropriate use of antimicrobial agents. Infants and children at risk for serious RSV infection should receive monthly doses of humanized murine anti-RSV monoclonal antibody throughout the RSV season (6). Infants and children at risk include 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 and those with hemodynamically significant heart disease, and 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., child care attendance, exposure to environmental pollutants, school-aged siblings, congenital abnormalities of the airways, or neuromuscular disease) during their first RSV season. Because the onset of RSV activity can vary between regions and communities, physicians and health-care facilities should consult their local clinical laboratories for the latest data on RSV activity (9).

Additional information and updates on RSV trends are available at

Reported by: National Respiratory and Enteric Virus Surveillance System collaborating laboratories. KJ Felton, I Pandya-Smith, MPH, AG Curns, MPH, AM Fry, MD, LJ Anderson, MD, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; NM Keeler, DVM, EIS Officer, 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. Welliver RC. Review of epidemiology and clinical risk factors for severe respiratory syncytial virus (RSV) infection. J Pediatr 2003;143 (5 Suppl):S112--7.
  3. Falsey AR, Walsh EE. Respiratory syncytial virus infection in adults. Clin Microbiol Rev 2000;13:371--84.
  4. Dowell SF, Anderson LJ, Gary HE Jr, et al. Respiratory syncytial virus is an important cause of community-acquired lower respiratory infection among hospitalized adults. J Infect Dis 1996;174:456--62.
  5. 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).
  6. 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(6 Pt 1):1447--52.
  7. 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.
  8. Weinberg GA, Erdman DD, Edwards KM, et al. Superiority of reverse-transcription polymerase chain reaction to conventional viral culture in the diagnosis of acute respiratory tract infections in children. J Infect Dis 2004;189:706--10.
  9. 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.

* 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 a mean percentage of specimens positive by antigen detection is >10%.

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.


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