Assessment of census-tract level socioeconomic position as a modifier of the relationship between short-term PM exposure and cardiovascular emergency department visits in Missouri.

Introduction: Ambient particulate matter ≤ 2.5 µm in aerodynamic diameter (PM) exposure elevates the risk for cardiovascular disease morbidity (CVDM). The aim of this study is to characterise which area-level measures of socioeconomic position (SEP) modify the relationship between PM exposure and CVDM in Missouri at the census-tract (CT) level.

Methods: We use individual level Missouri emergency department (ED) admissions data (n=3 284 956), modelled PM data, and yearly CT data from 2012 to 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 IQR changes in PM. In the second stage, we use multivariate metaregression to examine how CT-level SEP modifies the relationship between ambient PM exposure and CVDM.

Results: We find that overall, ambient PM exposure is associated with increased risk for CVDM. We test effect modification in statewide and urban CTs, 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 to 1.014)) compared with the lowest poverty CTs (OR=1.004 (95% CI 1.000 to 1.008)). Other SEP modifiers generally display an inconsistent or null effect.

Conclusion: Overall, we find some evidence that area-level SEP modifies the relationship between ambient PM exposure and CVDM, and suggest that the relationship between air-pollution, area-level SEP and CVDM may be sensitive to spatial scale.