Association between fine particulate matter (PM2.5) and infant mortality in a North Carolina birth cohort (2003-2015)

Background: While the association between fine particulate matter (PM2.5) and adult mortality is well established, few studies have examined the association between long-term PM2.5 exposure and infant mortality. Methods: We conducted an unmatched case-control study of 5992 infant mortality cases and 60,000 randomly selected controls from a North Carolina birth cohort (2003-2015). PM2.5 during critical exposure periods (trimesters, pregnancy, first month alive) was estimated using residential address and a national spatiotemporal model at census block centroid. We fit adjusted logistic regression models and calculated odds ratios (ORs) and 95% confidence intervals (CIs). Due to differences in PM2.5 over time, we stratified analyses into two periods: 2003-2009 (mean = 12.1 mu g/m(3), interquartile range [IQR]: 10.8-13.5) and 2011-2015 (mean = 8.4 mu g/m(3), IQR: 7.7-9.0). We assessed effect measure modification by birthing parent race/ethnicity, full-term birth, and PM2.5 concentrations. Results: For births 2003-2015, the odds of infant mortality increased by 12% (95% CI: 1.06, 1.17) per 4.0 mu g/m(3) increase in PM2.5 exposure averaged over the pregnancy. After stratifying, we observed an increase of 4% (95% CI: 0.95, 1.14) for births in 2003-2009 and a decrease of 15% (95% CI: 0.72, 1.01) for births in 2011-2015. Among infants with higher PM2.5 exposure (>= 12 mu g/m(3)) during pregnancy, the odds of infant mortality increased (OR: 2.69; 95% CI: 2.17, 3.34) whereas the lower exposure (<8 <mu>g/m(3)) group reported decreased odds (OR: 0.50; 95% CI: 0.28, 0.89). Conclusions: We observed differing associations of PM2.5 exposure with infant mortality across higher versus lower PM2.5 concentrations. Research findings suggest the importance of accounting for long-term trends of decreasing PM2.5 concentrations in future research.