State- and county-level income inequality and infant mortality in the USA in 2010: a cohort study.

Objectives: We examined the relationship between income inequality and the risk for infant/neonatal mortality at the state and county level and tested possible mediators of this relationship.
Methods: We first linked state and county Gini coefficients to US Vital Statistics 2010 Cohort Linked Birth and Infant Death records (n = 3,954,325). We then fit multilevel models to test whether income inequality was associated with infant/neonatal mortality. County-level factors were tested as potential mediators.
Results: Adjusted analyses indicated that income inequality at the county level-but not at the state level-was associated with increased odds of infant mortality (OR 1.14, 95% CI 1.10, 1.18) and neonatal death (OR 1.17, 95% CI 1.12, 1.23). Our mediators explained most of this variation. Bivariate analyses revealed associations between 3 county-level measures-patient-to-physician ratio, the violent crime rate, and sexually transmitted infection rate-and infant and neonatal mortality. Proportion of college-educated adults was associated with decreased odds for neonatal mortality.
Conclusions: Local variations in access to care, the rate of sexually transmitted disease, and crime are associated with infant mortality, while variations in college education in addition to these mediators explain neonatal mortality. To reduce infant and neonatal mortality, experiments are needed to examine the effectiveness of policies targeted at reducing income inequality and improving healthcare access, policing, and educational opportunities.