title: Air toxics and birth defects: a Bayesian hierarchical approach to evaluate multiple pollutants and spina bifida.
abstract: BACKGROUND
  While there is evidence that maternal exposure to benzene is associated with spina bifida in offspring, to our knowledge there have been no assessments to evaluate the role of multiple hazardous air pollutants (HAPs) simultaneously on the risk of this relatively common birth defect. In the current study, we evaluated the association between maternal exposure to HAPs identified by the United States Environmental Protection Agency (U.S. EPA) and spina bifida in offspring using hierarchical Bayesian modeling that includes Stochastic Search Variable Selection (SSVS).
  
  
  METHODS
  The Texas Birth Defects Registry provided data on spina bifida cases delivered between 1999 and 2004. The control group was a random sample of unaffected live births, frequency matched to cases on year of birth. Census tract-level estimates of annual HAP levels were obtained from the U.S. EPA's 1999 Assessment System for Population Exposure Nationwide. Using the distribution among controls, exposure was categorized as high exposure (>95(th) percentile), medium exposure (5(th)-95(th) percentile), and low exposure (<5(th) percentile, reference). We used hierarchical Bayesian logistic regression models with SSVS to evaluate the association between HAPs and spina bifida by computing an odds ratio (OR) for each HAP using the posterior mean, and a 95% credible interval (CI) using the 2.5(th) and 97.5(th) quantiles of the posterior samples. Based on previous assessments, any pollutant with a Bayes factor greater than 1 was selected for inclusion in a final model.
  
  
  RESULTS
  Twenty-five HAPs were selected in the final analysis to represent "bins" of highly correlated HAPs (ρ > 0.80). We identified two out of 25 HAPs with a Bayes factor greater than 1: quinoline (ORhigh = 2.06, 95% CI: 1.11-3.87, Bayes factor = 1.01) and trichloroethylene (ORmedium = 2.00, 95% CI: 1.14-3.61, Bayes factor = 3.79).
  
  
  CONCLUSIONS
  Overall there is evidence that quinoline and trichloroethylene may be significant contributors to the risk of spina bifida. Additionally, the use of Bayesian hierarchical models with SSVS is an alternative approach in the evaluation of multiple environmental pollutants on disease risk. This approach can be easily extended to environmental exposures, where novel approaches are needed in the context of multi-pollutant modeling.
authors.affiliation: Division of Biostatistics, University of Texas School of Public Health, Houston, TX, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Swartz
authors.affiliation: Division of Biostatistics, University of Texas School of Public Health, Houston, TX, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Cai
authors.affiliation: Division of Biostatistics, University of Texas School of Public Health, Houston, TX, USA.
authors.forename: Wenyaw
authors.initials: W
authors.lastname: Chan
authors.affiliation: Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, TX, USA.
authors.forename: Elaine
authors.initials: E
authors.lastname: Symanski
authors.affiliation: Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, TX, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Mitchell
authors.affiliation: Department of Pediatrics, Section of Hematology-Oncology and Texas Children's Cancer Center, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Danysh
authors.affiliation: Birth Defects Epidemiology and Surveillance Branch, Texas Department of State Health Services, Austin, TX, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Langlois
authors.affiliation: Department of Pediatrics, Section of Hematology-Oncology and Texas Children's Cancer Center, Baylor College of Medicine, Houston, TX, USA. Philip.Lupo@bcm.edu.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Lupo
mesh_terms: D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000633:toxicity*; D001499:Bayes Theorem; D004784:Environmental Monitoring; D005260:Female; D015386:Hazardous Substances / Q000633:toxicity*; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D008297:Male; D018811:Maternal Exposure; D008875:Middle Aged; D008962:Models, Theoretical; D016017:Odds Ratio; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology*; D015995:Prevalence; D016135:Spinal Dysraphism / Q000139:chemically induced / Q000453:epidemiology*; D013781:Texas / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D015386:Hazardous Substances