Objectives: In the present study, we evaluated hospital admissions for temperature-associated MI according to gender, age (<75 or ≥75 years), insurance type (National health Insurance (NHI) for the general population, or medical care (Medicaid) for the poor), and location (urban or rural) to compare the risks among these subpopulations. We also evaluated changes in threshold temperatures in summer and winter and correlated the findings with the risks of temperature-associated MI in the subpopulations.
Methods: We used National Health Insurance Service data for daily hospital admissions of MI, meteorological data from the Korea Meteorological Administration, and air pollution data from the National Institute of Environmental Research from 1 January 2004 to 31 December 2012. The generalized models analysis (GAM) was used to assess the short-term effects of temperature (mean, maximum and minimum thresholds) associated with MI admissions when temperatures increased above or decreased below the threshold temperature. The relationships were adjusted by humidity, barometric pressure at sea level, composition and amount of air pollutants (PM10, NO2, O3), day of the week, and duration of the heat wave or cold wave. We defined the threshold temperature as the change point detected using piecewise regression analysis with increased risk based on the relationship between temperature and MI admissions.
Results: An increased risk for hospital admission due to MI for several subpopulations was found when temperatures rose above or dropped below threshold temperatures. The threshold temperature and relative risks (RR) for MI were different according to subpopulations and season. In the summer, the threshold of mean temperatures ranged between 23.5°C to 28.5°C and the RRs ranged from 1.01 to 1.16 among the following subgroups: 1.16 (95% CI: 1.01-1.33) for the ≥75 years age group and 1.01 (95% CI: 0.96-1.05) for the <75 years age group, and 1.10 (95% CI: 1.02-1.20) for the urban population and 1.03 (95% CI: 0.95-1.12) for the rural population. The maximum temperature threshold ranged from 33.5°C to 34.5°C and the RRs ranged from 1.02 to 1.15 among the following subgroups: 1.08 RR (95% CI: 1.02-1.14) for the female group, 1.12 (95% CI: 1.01-1.24) for the ≥75 years age group, and 1.15 (95% CI: 1.04-1.28) for the Medicaid group. During winter, the RR of the Medicaid group was 1.05 (95% CI: 0.98-1.12) when the mean temperature dropped below threshold by -0.5°C. The RR was 1.11 (95% CI: 1.04-1.20) at temperatures below the minimum temperature threshold (-13.5°C). The RR of the urban population was 1.16 (95% CI: 1.02-1.32) and that of rural population was 1.04(95% CI: 1.00-1.08) when temperatures dropped below the minimum temperature threshold.
Conclusions: Significant increases in MI risk for several subgroups were associated with temperatures above or below the temperature threshold during summer and winter, respectively. In the summer, the female group, the ≥75 years age group, the Medicaid group, and the urban population showed the highest risk for MI when temperatures exceeded the mean and maximum temperature threshold. During winter, the Medicaid group and the urban population showed the highest risk for MI when temperatures dropped below the minimum temperature threshold. These findings identify vulnerable groups who are at increased risk for hospital admission due to MI that is related to climate change. The data can be used to establish climate change adaptation strategies for susceptible populations.
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