Associations between monthly fine particulate matter and ozone exposure, and postneonatal infant mortality in the...

Using NCHS birth and death records, we estimated associations between monthly mean fine particulate matter (PM_2.5) or ozone (O₃) concentrations during the postneonatal period (29-364 days) and postneonatal infant mortality (IM) among infants born between 2005 and 2017 in United States (U.S.) counties with >250,000 residents. Air quality data were derived from the U.S. EPA's EQUATES project, which fuses multi-year CMAQv5.3.2 model outputs with monitor measurements, spatially weighted to each county, and linked to birth and death records. We estimated incidence rate ratios and 95% confidence intervals using a hierarchical overdispersed Poisson regression model with random-effects. In stage one, climate-zone-specific models were adjusted for temperature and year. We then pooled estimates in stage two for a national estimate. There were 35,665,533 livebirths and 71,690 postneonatal deaths across 261 counties. Congenital anomalies (19.8%) and SIDS (16.8%) were leading causes. A 5 μg/m³ increase in monthly PM_2.5 exposure during the postneonatal period was associated with increased postneonatal IM for respiratory causes (1.06 [1.03, 1.10]) and SIDS (1.56 [1.30, 1.87]). A 10 ppb increase in O₃ exposure during the postneonatal period was associated with increased postneonatal IM for SIDS (1.31 [1.11, 1.55]). Associations between PM_2.5 and all-cause postneonatal IM were strongest in warm temperate zones, the Southwest, male infants, and infants born to younger and less educated mothers. For O₃, associations were highest for all-cause postneonatal IM in the West and infants born to younger and less educated mothers. Mean monthly PM_2.5 or O₃ exposure is associated with increased respiratory and SIDS-related postneonatal IM.