Case-control study of the risk factors linked to respiratory syncytial virus infection requiring hospitalization in premature infants born at a gestational age of 33-35 weeks in Spain

Background and Objective: The aim of this study was to identify those risk factors most likely to lead to the development of RSV-related respiratory Infection and subsequent hospital admission among premature infants born at 33-35 WGA (FLIP study) Methods: This was a prospective case-control study. Cases (186) hospitalized for respiratory syncytial virus (RSV) illness were recruited from 50 participating Spanish hospitals during the 20022003 RSV season (October 2002-April 2003). Controls (371) were selected in June 2003 but born at same time as cases. Results: Of these cases, 20.5% were admitted to the intensive care unit intensive care unit, and 7.6% required mechanical ventilation. None of the patients died. Conditional logistic regression analysis adjusted for medical center demonstrated that the risk of RSV-related respiratory infection requiring hospital admission in preterm infants 33-35 weeks of gestation (WGA) in Spain was most often associated with absolute chronologic age at start of RSV season less than or equal to10 weeks [ie, born between July 15 and December 15; odds ratio (OR), 3.95; 95% confidence interval (CI), 2.65-5.90], breast-feeding for less than or equal to2 months total (OR 3.26; 95% CI 1.96-5.42), presence of greater than or equal to1 school age siblings (OR 2.85; 95% CI 1.88-4.33), greater than or equal to4 residents and visitors at home (discounting school age siblings and the case/control him/herself) (OR 1.91; 95% CI 1.19-3.07) and a family history of wheezing (OR 1.90; 95% CI 1.19-3.01). Conclusions: In premature infants born 33-35 WGA, certain underlying risk factors significantly increase the risk of RSV-related respiratory infection and hospitalization. Premature infants 33-35 WGA with additional risk factors should be considered for RSV prophylaxis with palivizumab.