Does exposure of pregnant women to epidemic respiratory syncytial virus affect the severity of bronchiolitis?

Abstract Introduction Passive transplacental immunity against respiratory syncytial virus (RSV) appears to mediate in the protection of the infant for the first 6 months of life. Lower environmental exposure in pregnant women to RSV epidemic may influence the susceptibility of these infants to infection by lowering the levels of antibodies that are transferred to the fetus. Objectives To contrast the risk of severe disease progression in infants with acute bronchiolitis by RSV, according to the mother's level of exposure to epidemic. Method Retrospective cohort study of previously healthy infants with RSV-acute bronchiolitis during 5 epidemics was made. We compared the severity of the infection in those born during the period of risk (when is less likely the mother's exposure to epidemic and the transfer of antibodies to the fetus: October 15th–December 15th in our latitude) with the rest of acute bronchiolitis. Bivariate analysis was performed regarding birth in period of risk and the rest of variables, using the Chi-square test. Multivariate logistic regression analysis was performed to study possible classical confounding factors. Results 695 infants were included in the study. 356 infants were born during the period of risk . Of the 56 patients requiring admission to PICU, 40 of them (71.4%) were born in this period ( p = 0.002). In the multivariate analysis, the birth in the period of risk showed a 6.5 OR (95% CI: 2.13–19.7) independently of the rest of variables. Conclusions The worst clinical disease progression of the acute bronchiolitis by the RSV in less than 6 months age is related to lower exposure of the pregnant woman to the RSV epidemic.