Air Pollution and Postneonatal Infant Mortality in the United States, 1999-2002

Article excerpt

OBJECTIVE: Our goal was to evaluate the relationship between cause-specific postneonatal infant mortality and chronic early-life exposure to particulate matter and gaseous air pollutants across the United States.

METHODS: We linked county-specific monitoring data for particles with aerodiameter of [less than or equal to] 2.5 [micro]m ([PM.sub.2.5]) and [less than or equal to] 10 [micro]m ([PM.sub.10]), ozone, sulfur dioxide, and carbon monoxide to birth and death records for infants born from 1999 to 2002 in U.S. counties with > 250,000 residents. For each infant, we calculated the average concentration of each pollutant over the first 2 months of life. We used logistic generalized estimating equations to estimate odds ratios of postneonatal mortality for all causes, respiratory causes, sudden infant death syndrome (SIDS), and all other causes for each pollutant, controlling for individual maternal factors (race, marital status, education, age, and primiparity), percentage of county population below poverty, region, birth month, birth year, and other pollutants. This analysis includes about 3.5 million births, with 6,639 postneonatal infant deaths.

RESULTS: After adjustment for demographic and other factors and for other pollutants, we found adjusted odds ratios of 1.16 [95% confidence interval (CI), 1.06-1.27] for a 10-[micro]g/[m.sup.3] increase in [PM.sub.10] for respiratory causes and 1.20 (95% CI, 1.09-1.32) for a 10-ppb increase in ozone and deaths from SIDS. We did not find relationships with other pollutants and for other causes of death (control category).

CONCLUSIONS: This study supports particulate matter air pollution being a risk factor for respiratory-related postneonatal mortality and suggests that ozone may be associated with SIDS in the United States.

KEY WORDS: carbon monoxide, ozone, particulate matter air pollution, postneonatal infant mortality, respiratory-related deaths, sudden infant death syndrome, sulfur dioxide. Environ Health Perspect 116:110-115 (2008). doi:10. 1289/ehp.10370 available via http://dx.doi.org/ [Online 24 October 2007]

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Several studies have found a relationship between particulate matter (PM) air pollution and infant mortality in countries with relatively high levels of PM air pollution as well as in countries with lower pollution levels, such as Canada and the United States (Bobak and Leon 1999; Ha et al. 2003; Lipfert et al. 2000; Loomis et al. 1999; Ritz et al. 2006; Woodruff et al. 1997, 2006) These studies suggest that PM air pollution is more strongly associated with postneonatal mortality (deaths occurring after 28 days of life) than with neonatal mortality (deaths occurring up to 28 days of life) and that the association with postneonatal mortality appears to be specific to respiratory causes (Bobak and Leon 1999; Ha et al. 2003). However, a number of questions remain about the infant mortality and PM air pollution relationship and the role of other air pollutants as either potential confounders of the relationship or as independent predictors of infant mortality.

Until recently, most studies of air pollution and postneonatal infant mortality have focused on larger particles, either measured as total suspended particles or particles with an aerodiameter of [less than or equal to] 10 [micro]m [PM.sub.10]) (Bobak and Leon 1999; Ha et al. 2003; Lipfert et al. 2000; Ritz et al. 2006; Woodruff et al. 1997). Although monitoring of smaller particles measuring [less than or equal to] 2.5 [micro]m ([PM.sub.2.5]) [PM has become more widespread, only one study in California has evaluated [PM.sub.2.5] in relation to respiratory related infant mortality; results support a positive association (Woodruff et al. 2006). Although many studies in adults suggest that [PM.sub.2.5] is more strongly associated with respiratory and cardiovascular morbidity and mortality than [PM.sub.10], other studies have found larger particles to be important for certain outcomes (Brunekreef and Forsberg 2005; Pope and Dockery 2006). …