Correlation between respiratory syncytial virus (RSV) test data and hospitalization of children for RSV lower respiratory tract illness in Florida

Background: Florida experiences year-round outbreaks of respiratory syncytial virus (RSV), but it is unknown if there is a correlation between RSV virology data and disease-related hospitalizations. We analyzed RSV surveillance and hospitalization data for the state of Florida to determine if there is an association between seasonal virology data and the incidence of International Classification of Diseases, 9th revision, clinical modification (ICD-9-CM) coded hospitalizations for RSV lower respiratory tract illness. Methods: We conducted a retrospective analysis for each of 5 regions of Florida for 4 years (2001-2004) of monthly RSV surveillance data presented on the Florida Department of Health web-site and hospitalization data provided by the Agency for Health Care Administration. RSV was considered present when >= 10% of laboratory tests were positive in a given month and the duration of seasons was determined by the number of consecutive months threshold values were exceeded. Hospitalizations in children 24 months of age and younger were defined as RSV related if any of the following RSV-specific ICD-9-CM codes appeared on the discharge summary: 079.6 RSV; 466.11 acute bronchiolitis caused by RSV; and 480.1 pneumonia caused by RSV. Results: RSV circulated year-round statewide and seasons ranged from 7-8 months in the southwest, northwest, and north regions of Florida to 11-12 months in the central and southeast regions, respectively. More than 23,000 children younger than 24 months of age were hospitalized throughout the state for an RSV-related illness during the 4-year period, with almost 20,000 (86%) of the admissions in infants less than 12 months of age. There were 23 hospitalizations yearly per 1000 births and more than 90% of discharges occurred during the defined RSV seasons. Conclusions: To our knowledge, this is the first study to demonstrate a positive correlation between RSV test data and hospitalizations both statewide and for individual regions within Florida. It would be prudent for clinicians to obtain results of local RSV virology data to guide decisions on timing of prophylaxis to prevent RSV hospitalizations.