Acute exposure to fine and coarse particulate matter and infant mortality in Tokyo, Japan (2002-2013).

Few studies have evaluated the effect of short-term exposure to particulate matter (PM) less than 2.5μm in diameter (PM2.5) or to coarse particles on infant mortality. We evaluated the association between short-term exposure to PM and infant mortality in Japan and assessed whether adverse health effects were observable at PM concentrations below Japanese air quality guidelines. We used a time-stratified, case-crossover design. The participants included 2086 infants who died in the 23 urbanized wards of the Tokyo Metropolitan Government between January 2002 and December 2013. We obtained measures of PM2.5 and suspended particulate matter (SPM; PM<7μm in diameter) from one general monitoring station. As a measure of coarse particles, we calculated PM7-2.5 by subtracting PM2.5 from SPM. We then used conditional logistic regression to analyze the data. Same-day PM2.5 was associated with increased risks of infant and postneonatal mortality, especially for mortality related to respiratory causes. For a 10μg/m(3) increase in PM2.5, the odds ratios were 1.06 (95% confidence interval: 1.01-1.12) for infant mortality and 1.10 (1.02-1.19) for postneonatal mortality. PM7-2.5 was also associated with an increased risk of postneonatal mortality, independent of PM2.5. Even when PM2.5 and SPM concentrations were below Japanese air quality guidelines, we observed adverse health effects. This study provides further evidence that acute exposure to PM2.5 and coarse particles (PM7-2.5) is associated with an increased risk of infant mortality. Further, rigorous evaluation of air quality guidelines for daily average PM2.5 and larger particles is needed.