Identifying Risk Factors for Severe Respiratory Syncytial Virus Among Infants Born After 33 Through 35 Completed Weeks of Gestation: Different Methodologies Yield Consistent Findings

BACKGROUND:Prematurity is a proven risk factor for severe respiratory syncytial virus (RSV) infection. Prematurity leads to an increased need for, and duration of, hospital admission, intensive care, mechanical ventilation and supplemental oxygen, as well as increased mortality. METHODS:The Pediatric Investigators Collaborative Network on Infections in Canada (PICNIC) study was a prospective, multicenter, cohort study conducted in 16 regions across Canada during 2 successive RSV seasonsNovember 2000–June 2001, and November 2001–June 2002. The study regions were defined to capture all births and all hospital admissions. The FLIP [identify those risk Factors that most Likely may lead to development of RSV-related respiratory Infection and subsequent hospital admission among Premature infants born 33–35 weeks gestational age (GA)] study was a prospective, case-control study comparison of premature infants hospitalized for RSV infection and infants who had not been hospitalized to identify the risk factors that most likely would lead to development of RSV infection and subsequent hospital admission in this population. RESULTS:The overall hospitalization rate for RSV in the PICNIC study was 3.6% for infants of 33–35 weeks GA. In the FLIP study, the severity of RSV infection in the 33- to 35-week GA infants was similar to that in the younger infants of