title: Survival analysis of long-term exposure to different sizes of airborne particulate matter and risk of infant mortality using a birth cohort in Seoul, Korea.
abstract: BACKGROUND
  Several studies suggest that airborne particulate matter (PM) is associated with infant mortality; however, most focused on short-term exposure to larger particles.
  
  
  OBJECTIVE
  We evaluated associations between long-term exposure to different sizes of particles [total suspended particles (TSP), PM ≤ 10 μm in aerodynamic diameter (PM₁₀), ≤ 10-2.5 μm (PM(10-2.5)), and ≤ 2.5 μm (PM(2.5))] and infant mortality in a cohort in Seoul, Korea, 2004-2007.
  
  
  METHODS
  The study includes 359,459 births with 225 deaths. We applied extended Cox proportional hazards modeling with time-dependent covariates to three mortality categories: all causes, respiratory, and sudden infant death syndrome (SIDS). We calculated exposures from birth to death (or end of eligibility for outcome at 1 year of age) and pregnancy (gestation and each trimester) and treated exposures as time-dependent variables for subjects' exposure for each pollutant. We adjusted by sex, gestational length, season of birth, maternal age and educational level, and heat index. Each cause of death and exposure time frame was analyzed separately.
  
  
  RESULTS
  We found a relationship between gestational exposures to PM and infant mortality from all causes or respiratory causes for normal-birth-weight infants. For total mortality (all causes), risks were 1.44 (95% confidence interval, 1.06-1.97), 1.65 (1.18-2.31), 1.53 (1.22-1.90), and 1.19 (0.83-1.70) per interquartile range increase in TSP, PM₁₀, PM(2.5), and PM(10-2.5), respectively; for respiratory mortality, risks were 3.78 (1.18-12.13), 6.20 (1.50-25.66), 3.15 (1.26-7.85), and 2.86 (0.76-10.85). For SIDS, risks were 0.92 (0.33-2.58), 1.15 (0.38-3.48), 1.42 (0.71-2.87), and 0.57 (0.16-1.96), respectively.
  
  
  CONCLUSIONS
  Our findings provide supportive evidence of an association of long-term exposure to PM air pollution with infant mortality.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, USA.
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Son
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Bell
authors.forename: Jong-Tae
authors.initials: JT
authors.lastname: Lee
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007723:Korea; D008297:Male; D052638:Particulate Matter / Q000633:toxicity*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D016016:Proportional Hazards Models; D055815:Young Adult
chemical_list: D052638:Particulate Matter