GAITHERSBURG, MD—The number of infants hospitalized annually with acute bronchiolitis or pneumonia due to respiratory syncytial virus (RSV) infection has been estimated, but actual numbers have only recently become available. A new retrospective analysis shows that between 1997 and 1999, RSV bronchiolitis was the leading cause of hospitalization among infants younger than 1 year.[1]

Despite previous estimates of the impact of severe RSV infection, “no one had asked … ‘Where does RSV … rank among all the reasons why infants in the US are hospitalized?’ ” said Shelah Leader, PhD, Director of Pharmacoeconomics and Outcomes Research at MedImmune, Inc in Gaithersburg, Maryland. Her research demonstrated that “it ranked number one … for three years in a row.” MedImmune is the manufacturer of palivizumab, a passive immunization given as prophylaxis to infants at high risk for severe RSV.

Previous estimates of RSV hospitalization rates were based on hospital discharges of infants diagnosed with either bronchiolitis or pneumonia from unknown pathogens. Proportions estimated to be due to the virus during RSV season were then used to project hospitalization rates for RSV-related bronchiolitis and pneumonia.

The inception of specific diagnosis codes for RSV, combined with newer data from the 1997, 1998, and 1999 National Hospital Discharge Surveys, allowed Dr. Leader and colleague Kimmie Kohlhase, MS, to calculate that 297,684 (25.2 per 1,000) discharges of infants younger than 1 year had been hospitalized with a diagnosis of RSV between 1997 and 1999. Of these infants, 243,834 were diagnosed with RSV bronchiolitis, and 38,064 were diagnosed with RSV pneumonia. The annual rate of RSV hospitalization varied from 17.3 per 1,000 infants in 1998 to 26 per 1,000 in 1999. Periods of peak RSV hospitalization occurred during February of each of the three years studied.

RSV PASSIVE PROPHYLAXIS FOR AT-RISK INFANTS

“I’m hoping that this finding will help raise awareness of the seriousness of RSV as a health threat to infants,” Dr. Leader remarked. The American Academy of Pediatrics[2] has outlined a number of risk factors for which RSV prophylaxis is indicated. Dr. Leader noted, “Being premature elevates the risk of hospitalization.” Additionally, chronic lung disease (especially with oxygen dependency), exposure to tobacco smoke, and placement in day care are risk factors for RSV hospitalization.

Dr. Leader emphasized, “At this point, passive prophylaxis for high-risk infants is the only thing that is available and proven safe and effective” for combating hospitalization due to RSV in infants. Palivizumab, a recombinant humanized monoclonal antibody, and intravenous RSV immune globulin are the two agents approved for this purpose by the FDA.

—Mimi Zucker, PhD

References
1. Leader S, Kohlhase K. Respiratory syncytial virus-coded pediatric hospitalizations, 1997 to 1999. Pediatr Infect Dis J. 2002;21:629-632.
2. American Academy of Pediatrics Committee on Infectious Diseases and Committee on Fetus and Newborn. Prevention of respiratory syncytial virus infections: indications for the use of palivizumab and update on the use of RSV-IGIV. Pediatrics. 1998;102:1211-1216. [Accessed August 26, 2002.]

Return to table of contents