Background: Infants born at 33 through 35 completed weeks of gestation (33-35GA) are at risk for severe respiratory syncytial virus (RSV) infection, and palivizumab prophylaxis lowers hospitalizations for RSV infection by as much as 80%. The 33-35GA cohort comprises 3-5% of annual births; thus expert panels recommend limiting prophylaxis to situations in which frequency or health care impact of RSV infection is high. This study sought to identify independent risk factors for hospitalization for RSV infection.
Methods: This was a multicenter, prospective, observational cohort study of 33-35GA infants followed through their first RSV season (2001/2002 or 2002/2003). Baseline data were collected by interview with parents and review of medical records. Respiratory tract illnesses were identified by monthly phone calls, and medical records were reviewed for emergency room visits or hospitalizations. Risk factors were determined by stepwise logistic regression.
Results: Of 1,860 enrolled subjects, 1,832 (98.5%) were followed for at least 1 month, and 1,760 (94.6%) completed all follow-ups. Of 140 (7.6%) subjects hospitalized for respiratory tract illnesses, 66 infants had proven RSV infection. Independent predictors for hospitalization for RSV infection were: day-care attendance (odds ratio, 12.32; 95% confidence interval, 2.56, 59.34); November through January birth (odds ratio, 4.89; 95% confidence interval, 2.57, 9.29); preschool age sibling(s) (odds ratio, 2.76; 95% confidence interval, 1.51, 5.03); birth weight <10th percentile (odds ratio, 2.19; 95% confidence interval, 1.14, 4.22); male gender (odds ratio, 1.91; 95% confidence interval, 1.10, 3.31); > or = 2 smokers in the home (odds ratio, 1.87; 95% confidence interval, 1.07, 3.26); and households with >5 people, counting the subject (odds ratio, 1.79; 95% confidence interval, 1.02, 3.16). Family history of eczema (odds ratio, 0.42; 95% confidence interval, 0.18, 0.996) was protective.
Conclusions: Specific host/environmental factors can be used to identify which 33-35GA infants are at greatest risk of hospitalization for RSV infection and likely to benefit from palivizumab prophylaxis.