The effect of long-term exposure to air pollution and seasonal temperature on hospital admissions with cardiovascular and respiratory disease in the United States: A difference-in-differences analysis

Background: Few studies have simultaneously examined the effect of long-term exposure to air pollution and ambient temperature on the rate of hospital admissions with cardiovascular and respiratory disease using causal inference methods. Methods: We used a variation of a difference-in-difference (DID) approach to assess the effects of long-term exposure to warm-season temperature, cold-season temperature, NO₂, O₃, and PM_2.5 on the rate of hospital admissions for cardiovascular disease (CVD), myocardial infarction (MI), ischemic stroke, and respiratory diseases from 2001 to 2016 among Medicare beneficiaries who use fee-for-service programs. We computed the rate of admissions by zip code and year. Covariates included demographic and socioeconomic variables which were obtained from the decennial Census, the American Community Survey, the Behavioral Risk Factor Surveillance System, and the Dartmouth Health Atlas. As a secondary analysis, we restricted the analysis to zip code-years that had exposure to low concentrations of our pollutants. Results: PM_2.5 was associated with a significant increase in the absolute rate of annual admissions with cardiovascular disease by 47.71 admissions (95 % CI: 41.25–56.05) per 100,000 person-years, myocardial infarction by 7.44 admissions (95 % CI: 5.53–9.63) per 100,000 person-years, and 18.58 respiratory admissions (95 % CI: 12.42–23.72) for each one μg/m³ increase in two-year average levels. O₃ significantly increased the rates of all the studied outcomes. NO₂ was associated with a decreased rate of admissions with MI by 0.83 admissions (95 % CI: 0.10–1.55) per 100,000 person-years but increased rate of admissions for respiratory disease by 3.16 admissions (95 % CI: 1.34–5.24) per 100,000 person-years. Warmer cold-season temperature was associated with a decreased admissions rate for all outcomes. Conclusion: Air pollutants, particularly PM_2.5 and O₃, increased the rate of hospital admissions with cardiovascular and respiratory disease among the elderly, while higher cold-season temperatures decreased the rate of admissions with these conditions.