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

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Abstract
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) 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 2002–2003 RSV season (October 2002–April 2003). Controls (371) were selected in June 2003 but born at same time as cases. 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 ≤10 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 ≤2 months total (OR 3.26; 95% CI 1.96–5.42), presence of ≥1 school age siblings (OR 2.85; 95% CI 1.88–4.33), ≥4 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). 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.