Matched case-control study of air pollution and infant mortality in North Carolina

Infant mortality is an indicator of overall population health but has been evaluated in relatively few studies of air pollution. We estimated associations between postnatal exposure to air pollution and postneonatal infant mortality in a North Carolina birth cohort.

We identified cases of infant mortality with dates of birth between 2003 and 2015. For each case, we randomly selected 10 controls from at-risk infants without replacement, matched on year of birth and geographic region. Air pollutant concentrations - fine particulate matter (PM_2.5); 5 PM_2.5 components; nitrogen dioxide (NO₂); and ozone (O₃) - were assigned to each day between birth and death for cases and averaged for postnatal exposure. Controls were assigned exposure for the same number of postnatal days as matched cases. We estimated adjusted odds ratios (ORs) and 95% confidence intervals (CIs) using conditional logistic regression models.

We observed a positive association between postnatal PM_2.5 exposure and postneonatal infant mortality (OR [95%CI]: 1.08 [0.97, 1.21]). For cause-specific postneonatal infant mortality, PM_2.5 associations were stronger for cardiovascular (1.65 [1.11, 2.45]) and respiratory deaths (1.45 [0.94, 2.25]). PM_2.5 components generally followed similar patterns. NO₂ and O₃ showed elevated associations with postneonatal infant mortality due to congenital heart defects and cardiovascular or respiratory causes. O₃ was also positively associated with deaths due to SIDS.

Our results underscore infants with pre-existing conditions as particularly at risk to the effects of air pollution. Additional research and public health messaging are important for addressing this threat to children's health.