Familial susceptibility to severe respiratory infection in early life.

Lower respiratory tract infections (LRTI) are common in the first year of life and are mostly caused by viruses. Severity of LRTI in infants is associated with early-life environmental factors. Genetic association studies also suggest a role of heredity in susceptibility to acute bronchiolitis. We designed a case control study to further investigate relative importance of familial influences in risk of LRTI in early childhood compared to environmental factors. From a hospital database, we selected 1,308 children (436 cases; 872 controls) living in Oxfordshire. Cases were children under age 5 years admitted to hospital with LRTI. Parental history and other exposures were recorded in cases and controls by postal questionnaire. Maternal history of asthma increased the risk of severe LRTI in the first year of life, independent of subsequent asthma in a child. History of maternal bronchiolitis also increased the risk of infant LRTI. These results further support the possibility that genetic factors play an important role in susceptibility to severe viral respiratory infections in early life, and suggest that this effect may be independent of subsequent childhood asthma.