Brief Report: Respiratory Syncytial Virus Activity --- United States, 2005--2006

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections (LRTIs) (e.g., bronchiolitis and pneumonia) among young children in the United States (1). RSV also causes severe respiratory disease and a substantial number of deaths among older adults (2) and persons with compromised respiratory, cardiac, or immune systems (3). RSV is transmitted person to person through close contact or inhalation of large droplets from a sneeze or cough; infection also can occur through contact with fomites (i.e., contaminated surfaces or objects). In temperate climates, peak RSV activity typically occurs during the winter. This report presents preliminary data on RSV activity reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS) for the weeks ending July 8--November 18, 2006, indicating the onset of the 2006--2007 RSV season, and summarizes RSV trends during July 2005--June 2006. Health-care providers should consider RSV in the differential diagnosis for persons of all ages with LRTIs and implement appropriate isolation precautions to prevent nosocomial transmission from RSV-infected patients (4). Immune prophylaxis should be considered for certain infants and young children at high risk for complications from RSV infection (e.g., certain premature infants or infants and children with chronic lung and heart disease) (5).

NREVSS is a laboratory-based passive surveillance system that monitors temporal and geographic trends for several respiratory and enteric viruses. The laboratories report weekly to CDC the number of specimens tested for viral pathogens, including RSV, and number of positive test results. During July 2005--June 2006, a total of 71 clinical and public health laboratories in 39 states* and the District of Columbia reported RSV data and are included in this analysis. Eighteen laboratories were excluded because of inconsistent reporting or reporting fewer than 35 weeks of data. A total of 120,503 tests were performed, and 19,533 (16.2%) were positive by antigen-detection testing. National RSV activity^† began the week ending November 19, 2005, and continued for 21 weeks until April 1, 2006.

Data were summarized by region (West, East, South, and Central) except those from Florida. Data from Florida came from three laboratories (two in Miami and one in Orlando) and were presented separately because they differed substantially from RSV-detection data from the remainder of the South region (Figure). Regional RSV activity^§ was highest during October for Florida, during late December and early January for the South (27 laboratories reporting), during January for the Northeast and Midwest (19 laboratories reporting), and during February for the West (15 laboratories reporting). The Florida RSV season seems similar to those reported from some tropical settings in the Northern Hemisphere (6).

Although 17,736 (91%) RSV detections were reported during November 12, 2005--April 15, 2006, sporadic detections were reported throughout the year. During mid-April through September 2006, laboratories in 36 states and the District of Columbia reported 1,072 RSV detections; of these, 511 (48%) were from Florida. Additional data from Florida laboratories not participating in NREVSS are available at http://www.doh.state.fl.us/disease_ctrl/epi/RSV/rsv.htm.

For the current reporting period (July 8--November 18, 2006), 62 laboratories in 37 states reported testing for RSV. Preliminary 2006 data suggest that the annual seasonal peak began in Florida during the week ending July 1, in the rest of the South during the week ending October 14, and in the Northeast during the week ending November 11 (Figure).

Health-care providers should consider RSV as a cause of acute respiratory disease in all age groups during the annual seasonal peak. Because the onset of RSV activity can vary among regions and communities, physicians and health-care facilities can consult their local clinical laboratories for the latest data on RSV activity. Although several tests can be used to detect RSV infection in young children, only sensitive reverse transcription--polymerase chain reaction (RT-PCR) assays are sufficient to reliably detect RSV in older children and adults (7). NREVSS expanded reporting to include RT--PCR testing for RSV in 2004. However, these data are not included in the annual summary because of the limited number of laboratories reporting RT--PCR results.

Currently, no vaccine or effective therapy is available for RSV. Infants and children at risk for serious RSV infection can receive immune prophylaxis with monthly doses of a humanized murine anti-RSV monoclonal antibody during the RSV season. Infants and children at risk include those aged <24 months with chronic lung disease who have required medical 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., day care attendance, exposure to environmental pollutants, school-aged siblings, congenital abnormalities of the airways, or neuromuscular disease) during their first RSV season (5). Additional information and updates on RSV national and regional trends are available at http://www.cdc.gov/ncidod/dvrd/revb/nrevss/index.htm.

Reported by: National Respiratory and Enteric Virus Surveillance System collaborating laboratories. AL Fowlkes, AM Fry, MD, LJ Anderson, MD, Div of Viral Diseases, National Center for Immunization and Respiratory Diseases (proposed), CDC.

References

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. 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.
3. 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.
4. 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).
5. 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.
6. Weber MW, Mullholland EK, Greenwood BM. Respiratory syncytial virus infection in tropical and developing countries. Top Med Int Health 1998;3:268--80.
7. 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.

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

^† National RSV activity is defined as the first of 2 consecutive weeks during which 50% of participating laboratories report RSV detections and the mean percentage of specimens positive by antigen detection is >10%.

^§ Regional RSV onset and conclusion are defined by NREVSS as the median date that indicates the first of 2 consecutive weeks a participating laboratory reports >10% of specimens testing positive by antigen detection and the last week of >10% positive tests preceding 2 consecutive weeks of <10% positive tests.

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Date last reviewed: 11/29/2006