Council on Environmental Health
Article Review

Prepared by: Helen J. Binns, MD, MPH
January 2008

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

AUTHORS
Woodruff TJ, Darrow LA, Parker JD

FROM
University of California, Emory University, and National Center for Health Statistics

CITATION
Environ Health Perspect 2008;116:110-5

WEB LINK
http://www.ehponline.org/members/2007/10370/10370.pdf

OVERVIEW
This paper evaluates influences of multiple air pollution on post-neonatal infant deaths (defined as deaths between age 28 days to 1 year) from all causes, respiratory causes, and SIDS. 

CONTEXT
Past studies suggest that air PM (particulate matter) concentrations influence infant mortality in countries with high levels of such pollution and those with lower levels.  Studies examining relationship of infant mortality with other air pollutants (CO, SO2, NO2) have varied but generally significant associations were not found.  The relationship between SIDS and air pollutants has also been examined, with some studies reporting positive associations between SIDS and PM10 (particles with aerodiameter of £10 mm), NO2 and SO2.

WHAT DID THEY DO?
They evaluated data from the National Center for Health Statistics that included birth certificate and post-neonatal infant death linked data (restricted to singleton birth and death in same county). Data were also restricted to births in counties with at least 250,000 residents and known parental demographic status.  Data from PM10, PM2.5, ozone, CO, and SO2 were obtained from EPA monitoring sites matched to mother’s county of residence.  Average concentrations of each pollutant over the first 2 months of life were used as measures of chronic exposure.  For the study population, the median PM10 was about 29 mg/m3 (inter-quartile range 23-34 mg/m3) and median O3 was about 27 PPB (inter-quartile range 20-32 PPB)   Analyses used logistic regression with general estimating equations (to account for correlated data – in this case pollution exposures and census-level covariates).  Variables were included in the models to reduce effects from: time trends; season; region of the US; and neighborhood-level SES.  Single-pollutant and multi-pollutant models were developed.

WHAT DID THEY FIND?
The study cohort includes about 3.5 million infants from the 16 million born in the US during 1999-2002.  There were about 6,600 deaths analyzed (including about 9% respiratory causes, 21% SIDS, and 11% “ill-defined” cause).  Respiratory-related cause of death was significantly positively related to PM10 in single-pollutant and multi-pollutant models, with increase of 16% for PM10 increase of 10 mg/m3.  Data suggest a positive relationship between O3 pollutant levels and SIDS deaths in both single- and multi-pollutant models, particularly when analyses were limited to deaths in the first 90 days of life. 

CONSIDERATIONS
Infants with “ill-defined” cause of death complicate the cause-specific analyses.  Prenatal air pollution exposures, which may increase risk of peri-natal outcomes, are not accounted for in this study.

WHAT DOES THIS MEAN?
In urban areas like those in this study, air pollutants influence infant death from respiratory causes and SIDS.  Continued monitoring and development and application of measures to reduce air pollutants are needed.

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