Variability in severity among different respiratory syncytial virus (RSV) seasons may influence hospital admission rates for RSV-induced lower respiratory tract infection (LRTI) in young children. The aim of the present study was to identify through logistic regression analysis, risk factors associated with higher likelihood to acquire RSV-induced LRTI, in children with symptoms severe enough to lead to hospital admission. Over four consecutive RSV seasons (2000-2004), records from children <4 years of age admitted for RSV-induced LRTI ("cases") were compared with those from children with LRTI not due to RSV and not requiring hospitalization ("controls"). 145 "case-patients" and 295 "control-patients" were evaluated. Independent from the severity of the four epidemic seasons, seven predictors for hospitalization for RSV infection were found in the bivariate analysis: number of children in the family, chronological age at the onset of RSV season, birth weight and gestational age, birth order, daycare attendance, previous RSV infections. In the logistic regression analysis, only three predictors were detected: chronological age at the beginning of RSV season [aOR =8.46; 95% CI:3.09-23.18]; birth weight category [aOR =7.70; 95% CI:1.29-45.91]; birth order (aOR =1.92; 95% CI:1.21-3.06).
Conclusions: Independent from the RSV seasonality, specific host/environmental factors can be used to identify children at greatest risk for hospitalization for RSV infection.