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 2.5 μm in diameter (PM_2.5) 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 PM_2.5 and suspended particulate matter (SPM; PM <7 μm in diameter) from one general monitoring station. As a measure of coarse particles, we calculated PM_7-2.5 by subtracting PM_2.5 from SPM. We then used conditional logistic regression to analyze the data. Same-day PM_2.5 was associated with increased risks of infant and postneonatal mortality, especially for mortality related to respiratory causes. For a 10 μg/m³ increase in PM_2.5, 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. PM_7-2.5 was also associated with an increased risk of postneonatal mortality, independent of PM_2.5. Even when PM_2.5 and SPM concentrations were below Japanese air quality guidelines, we observed adverse health effects. This study provides further evidence that acute exposure to PM_2.5 and coarse particles (PM_7-2.5) is associated with an increased risk of infant mortality. Further, rigorous evaluation of air quality guidelines for daily average PM_2.5 and larger particles is needed.