Wildfire Smoke Exposure and Cardiovascular-related Effects Among the Medicare Population: A Case-crossover Study of the 2017 California Wildfire Season Open Access

Abstract

Wildfire smoke is a significant source of exposure to elevated levels of fine particulate matter (PM2.5), although the health effects of wildfire smoke have not been studied extensively. Previous epidemiological studies have reported inconsistent results for the cardiovascular-related health impacts associated with wildfire smoke exposure. A population-based analysis was conducted to estimate associations between incident cardio- and cerebrovascular events among the Medicare population and exposure to smoke density based on estimated concentrations of PM2.5, comparing wildfire smoke days to non-smoke days in California during the 2017 wildfire season. A case-crossover design was applied using conditional logistic regression to compare ZIP code levels of smoke density (1 – light, 2 – moderate, and 3 – heavy) on case days and 3-4 control days, matched by day of the week and month, before and after the case day. Separate analyses were performed to examine exposure lag periods, 0-4 days before the case day. Subgroup analyses were performed by sex, race, ethnicity, age group (≤69, 70-74, 75-79, 80-84, 85-89, 90-94, ≥95), and Medicaid eligibility. No increased risk was observed for ischemic heart disease, congestive heart failure, COPD, acute myocardial infarction, or atrial fibrillation across all 0-4 lag days, after adjusting for temperature and relative humidity. A marginally significant increased risk of ischemic stroke was associated with the lagged effects of exposure to light density smoke at lag 1 (OR: 1.05, 95% CI: 1.01, 1.10), lag 3 (OR: 1.07, 95% CI: 1.02, 1.12), and lag 4 (OR: 1.07 (95% CI: 1.02, 1.12). For women, effect estimates for light smoke density were significantly higher at lag 1 (OR: 1.12, 95% CI: 1.05, 1.19 vs OR: 0.99, 95% CI: 0.92, 1.06). No significant differences were observed by age, race, ethnicity, or Medicaid eligibility at lag 0-4. These findings suggest evidence of a marginal increase in odds of ischemic stroke associated with previous-day, 3-day, and 4-day light density smoke exposure. Further research is needed to characterize better the extent to which cardiovascular and cerebrovascular effects are associated with wildfire smoke exposure among older adults and determine who among the population may be most susceptible to wildfire-related air pollution.

Table of Contents

Table of Contents

Acknowledgment................................................................................................................1

Introduction .........................................................................................................................1

Methods................................................................................................................................2

Study Population and Health Data .................................................................................................2

Exposure Data...............................................................................................................................3

Meteorological Data ......................................................................................................................4

Exposure Assessment.....................................................................................................................4

Statistical Analysis................................................................................................................5

Results ..................................................................................................................................6

Discussion.............................................................................................................................8

Conclusion..........................................................................................................................12

References ..........................................................................................................................13

Tables and Figures .............................................................................................................17 

About this Master's Thesis

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School	Rollins School of Public Health
Department	Environmental Health
Degree	M.P.H.
Submission	Master's Thesis
Language	English
Research Field	Environmental Health
Keyword	Wildfire-attributable particulate matter English PM2.5 Smoke exposure Wildfire Air pollution
Committee Chair / Thesis Advisor	Liuhua Shi, ScD, Emory University

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