Long-term PM2.5 exposure and sepsis mortality in a US medicare cohort

Abstract

Background: Risk factors contributing to sepsis-related mortality include clinical conditions such as cardiovascular disease, chronic lung disease, and diabetes, all of which have also been shown to be associated with air pollution exposure. However, the impact of chronic exposure to air pollution on sepsis-related mortality has been little studied. METHODS: In a cohort of 53 million Medicare beneficiaries (228,439 sepsis-related deaths) living across the conterminous United States between 2000 and 2008, we examined the association of long-term PM_2.5 exposure and sepsis-related mortality. For each Medicare beneficiary (ages 65-120), we estimated the 12-month moving average PM_2.5 concentration for the 12 month before death, for their ZIP code of residence using well validated GIS-based spatio-temporal models. Deaths were categorized as sepsis-related if they have ICD-10 codes for bacterial or other sepsis. We used Cox proportional hazard models to assess the association of long-term PM_2.5 exposure on sepsis-related mortality. Models included strata for age, sex, race, and ZIP code and controlled for neighborhood socio-economic status (SES). We also evaluated confounding through adjustment of neighborhood behavioral covariates.

Results: A 10 μg/m³ increase in 12-month moving average PM_2.5 was associated with a 9.1% increased risk of sepsis mortality (95% CI: 3.6-14.9) in models adjusted for age, sex, race, ZIP code, and SES. HRs for PM_2.5 were higher and statistically significant for older (> 75), Black, and urban beneficiaries. In stratified analyses, null associations were found for younger beneficiaries (65-75), beneficiaries who lived in non-urban ZIP codes, and those residing in low-SES urban ZIP codes.

Conclusions: Long-term PM_2.5 exposure is associated with elevated risks of sepsis-related mortality.

Keywords: Air pollution; Chronic exposure; Particulate matter; Sepsis.

Fig. 1

Mortality hazard ratios* (95% CI) associated with a 10 μg/m3 increase in 12-month average PM2.5 and non-traffic PM2.5† for entire population and by subgroup, US 2000—2008. Abbreviations: CI Confidence interval, PM_2.5 Particles with aerodynamic diameters < 2.5 μm, BRFSS Behavioral Risk Factor Surveillance System. ^* Estimated using Cox PH models with strata for age (1 year age categories with 90 + year old as one category), sex (male, female), race (white, non-white) and ZIP Code (38,715 ZIP codes), adjusted for ZIP code and state SES. ^† While all participants had valid PM_2.5 measures assigned to their ZIP code of residence, NO₂ estimates were available only for 91.2% of the Medicare population