Background: Acute respiratory infections (ARIs) occur more commonly in children attending out-of-the-home child care. However, it is not known what determinants contribute to that risk. Kamper-Jørgensen and colleagues sought to determine which family and child characteristics placed children attending day care at the highest risk of ARI.

The Study: This cohort study used comprehensive data to track day care enrollment and attendance in 266 Danish municipalities over 15 years. The investigators also tracked hospitalizations of children admitted for ARIs (including upper and lower respiratory infections) during the study period. Incidence rate ratios were used to evaluate the impact of day care attendance on ARIs. The investigators controlled for age, length of enrollment, types and size of child care facility, season, geographic location, and other demographic variables.

Results: During the study, there were 138,821 hospitalizations for ARI among children zero to five years of age. Of these, 34 percent occurred in children younger than one year, 28 percent occurred in one-year-olds, 14 percent in two-year-olds, 10 percent in three-year-olds, 8 percent in four-year-olds, and 6 percent in five-year-olds. About two thirds of children were admitted once; smaller percentages were admitted two and three times. Compared with children cared for at home, day care attendees up to three years of age had a higher risk of hospitalization for ARI, with a decreasing risk as age increased. For children six months of age, the incidence rate ratio was 79 percent higher for day care attendees than for children cared for at home. By the time the children were one year of age, the excess risk was down to 44 percent. Risks were highest in children just starting day care. The longer they were enrolled, the lower the risk of hospitalization for ARI, with enrollment at or exceeding 12 months carrying no greater risk than the risk for children cared for at home.

Other findings showed that children from facilities that cared for children of a similar age had slightly higher hospitalization risk than day cares with integrated ages. Children living in homes where there were no other children younger than five years had markedly higher hospitalization risk when they attended day care than those with other preschool-age household members. The investigators calculated that if none of the children in the cohort attended day care, 11 percent of ARI hospitalizations could have been avoided.

Conclusion: The authors conclude that, overall, increased risk of hospitalization for ARI occurred in the youngest children (zero to two years of age), especially in the first months of enrollment and in children with no other small children in the home. The authors suggest that keeping children at home during the first year of life may be beneficial. Barring that option, enrolling children in family-style day care or an age-integrated facility could be modestly protective.