Respiratory syncytial virus risk factors in late preterm infants.

The key role of respiratory syncytial virus (RSV) in causing infant morbidity and hospitalizations is worldwide well recognized. The late preterm infants (34-36 weeks of gestational age (WGA)) showed a higher risk of hospitalization for RSV-induced infection as compared with full-term infants and similar to that seen in very preterm infants. In addition to the prematurity, a number of risk factors have been identified in 33-35 WGA infants that are associated with RSV-hospitalization as demonstrated by the Canadian and the Spanish studies. However, prematurity per se is not the only factor, since RSV-hospitalization in the first year of life also occurs in numerous full-term and previously healthy infants. Indeed, a recent case-control study on mostly full-term children showed that chronological age at the beginning of RSV season, low birth weight, and birth order (>or=1 sibling) were associated with a higher likelihood to acquire RSV-induced LRTI, severe enough to lead to hospital admission. In order to maximize the cost effectiveness of immunoprophylaxis with palivizumab, the American Academy of Pediatrics have recently updated recommendations resulting in a restriction of its use to infants at highest risk of hospitalization during times when RSV is most likely to be circulating (i.e. in the first 3 months of life for late preterm infants). According to a variety of epidemiologic data in this gestational age group, the risk of exposure should include day-care attendance and having a sibling <5 years of age. However, in an Italian study, in addition to chronological age at the beginning of RSV season, birth weight and birth order were significant predictors for RSV infection with hospitalization. On the basis of the finding that among nations the difference for severe RSV may exist in environmental and demographic risk factors, an 'International' tool has been developed based on the data from the Spanish FLIP study to predict the likelihood of RSV-hospitalization in newborns 33-35 WGA.