The association of home characteristics and risk of respiratory tract infections and acute otitis media in the first 18 months of life: a study of ~ 48 000 children in the Danish National Birth Cohort

Respiratory tract infections (RTIs) and acute otitis media (AOM) in the first 18 months of life have a large societal and individual impact and household conditions may be important in primary prevention thereof. To assess protective and harmful prenatal home exposures on RTIs and AOM in the first 18 months of life. We included complete cases from the Danish National Birth Cohort. Prenatal exposure and confounder data and outcome data gathered through questionnaire-based interviews at ~ 6 months and ~ 18 months were linked with routinely collected registry data. We built Poisson regression models with robust standard errors for dichotomous outcomes of pneumonia, AOM, bronchitis, and common cold at 6 months and 18 months. We report incidence rate ratios (aIRRs) and 95% confidence intervals (CI) for associations between home ownership, space per child, living on a farm with livestock, and pets. Home ownership was not associated with any outcomes, except for frequent common cold (other vs. own, aIRR 1.07[1.01, 1.14]). Household crowding as measured by less space per child was strongly associated with pneumonia and AOM at 6 months, in an exposure-dependent manner. However, the direct effect of increasing space itself was likely less important than the direct effect of the number of other children in the home. We observed no protective effect of dogs or cats, or farmhouse living with livestock on outcomes at 6 months. However, living in a farmhouse with livestock was associated with small risk reductions of pneumonia, AOM, and frequent common colds at 18 months. Post hoc analyses suggested that any benefit may be due to farm characteristics associated with cows, and any potential harm was associated with poultry. Crowding is associated with greater risks of RTIs in the first months of life, although the association is largely driven by number of children in the home, rather than space per se. Risks associated with living on a farm depend on the type of livestock. Other factors like home ownership and pets are potentially unimportant.