Objectives: The purpose of this study was to assess the role of siblings in day care as a determinant of infants' risk of lower respiratory tract infections.
Methods: A total of 3238 children (86%) out of 3754 Oslo, Norway, newborns recruited in 1992/93 were followed for 1 year.
Results: In logistic regression analysis, the risk of infection was increased in (1) infants with one or more siblings compared with infants without siblings (adjusted odds ratio [OR] = 2.3; 95% confidence interval [CI] = 1.84, 2.85) and (2) infants with one or more siblings in day care compared with infants with siblings not in day care (adjusted OR = 1.7; 95% CI = 1.21, 2.26).
Conclusions: The results suggest that siblings in day care outside the home increase infants' risk of lower respiratory tract infections.