An assessment of census-tract level socioeconomic position as a modifier of the relationship between PM 2.5 concentrations and cardiovascular emergency department visits in Missouri

Ambient PM2.5 exposure elevates the risk for cardiovascular disease morbidity (CVDM). The aim of this study is to characterize which area-level measures of socioeconomic position (SEP) modify the relationship between PM2.5 exposure and CVDM in Missouri at the census-tract (CT) level. We use individual level Missouri emergency department (ED) admissions data (n = 3,284,956), modeled PM2.5 data, and yearly census tract data from 2012-2016 to conduct a two-stage analysis. Stage one uses a case-crossover approach with conditional logistic regression to establish the baseline risk of ED visits associated with interquartile range (IQR) changes in PM2.5. In the second stage, we use multivariate meta-regression to examine how census tract level SEP modifies the relationship between ambient PM2.5 exposure and CVDM. We find that overall, ambient PM2.5 exposure is associated with increased risk for CVDM. We test effect modification in statewide and urban census tracts, and in the warm-season only. Effect modification results suggest that among SEP measures, poverty is most consistently associated with increased risk for CVDM. For example, across Missouri the highest poverty CTs are at an elevated risk for CVDM [OR = 1.010 (95% CI 1.007, 1.014)] compared to the lowest poverty CTs [OR = 1.004 (95% CI 1.000, 1.008)]. Other SEP modifiers generally display an inconsistent or null effect. Overall, we find some evidence that area-level SEP modifies the relationship between ambient PM2.5 exposure and CVDM, and suggest that the relationship between air-pollution, area-level SEP, and CVDM may be sensitive to spatial scale.