Long-term Exposure to Ambient PM2.5 and Hospitalizations for Myocardial Infarction among U.S. Residents: A Difference-in-Differences Analysis

BackgroundAir pollution has been recognized as an untraditional risk factor for myocardial infarction (MI). However, the MI risk attributable to long-term exposure to fine particulate matter (PM2.5) is unclear, especially in younger populations, and few studies represented the general population. MethodsWe applied the difference-in-differences approach to estimate the relationship between annual PM2.5 exposure and hospitalizations for MI among U.S. residents and further identified potential susceptible subpopulations. All hospital admissions for MI in ten U.S. states over the period 2002-2016 were obtained from the Healthcare Cost and Utilization Project State Inpatient Database. ResultsIn total, 1,914,684 MI hospital admissions from 8,106 ZIP codes in ten states from 2002 to 2016 were included in this study. We observed a 1.35% (95% CI: 1.11-1.59%) increase in MI hospitalization rate for 1 g/m3 increase in annual PM2.5 exposure. The estimate was robust to adjustment for surface pressure, relative humidity and co-pollutants. In the population with exposure at or below 12 g/m3, there was a larger increment of 2.17% (95% CI: 1.79-2.56%) in hospitalization rate associated with 1 g/m3 increase in PM2.5. Young people (0-34 years) and elderly people ([≥]75 years) were the two most susceptible age groups. Residents living in more densely populated or poorer areas and individuals with comorbidities were observed to be at a greater risk. ConclusionsThis study indicates long-term residential exposure to PM2.5 could lead to increased risk of MI among U.S. general population. The association persists below current standards. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LILong-term exposure to PM2.5 increased the risk of myocardial infarction in the general U.S. population. C_LIO_LIYoung individuals aged 0-34 years had the highest relative risk from long-term exposure to PM2.5, and elderly people aged [≥]75 years were the second most susceptible to the effects. C_LIO_LIIndividuals with iron deficiency anemia, psychosis, and renal failure were more susceptible to the long-term effects of PM2.5 on MI. C_LI What are the clinical implications?O_LILong-term PM2.5 exposure is one of the important modifiable environmental risk factors for myocardial infarction, therefore, air pollution control and behavioral interventions should be taken to prevent the occurrence of myocardial infarction. C_LI