title: High-temperature indices associated with mortality and outpatient visits: characterizing the association with elevated temperature.
abstract: This study aimed to identify optimal high-temperature indices to predict risks of all-cause mortality and outpatient visits for subtropical islanders in warm seasons (May to October). Eight high-temperature indices, including three single measurements (average, maximum and minimum temperature) and five composite indices (heat index, humidex, temperature humidity index, apparent temperature and wet-bulb globe temperature), and their standardized Z scores, were used in distributed lag non-linear models. Cumulative 8-day (lag zero to seven days) relative risks (RRs) and 95% confidence intervals were estimated, 1 and 2 standardized deviations above the medium (i.e., at 84.1th and 97.7th percentile, respectively), by comparing with Z scores for the lowest risks of mortality and outpatient visits as references. Analyses were performed for Taipei in north, Central Taiwan and Southern Taiwan. Results showed that standardized Z-values of high-temperature indices associated with the lowest health risk were approximately 0 in Taipei and Central Taiwan, and -1 in Southern Taiwan. As the apparent temperature was at Z=2, the cumulative 8-day mortality risk increased significantly, by 23% in Taipei and 28% in Southern Taiwan, but not in Central Taiwan. The maximum temperature displayed consistently a high correlation with all-cause outpatient visits at Z=1; with the cumulative 8-day RRs for outpatient visits increased by 7%, 3%, and 4% in the three corresponding areas. In conclusion, this study has demonstrated methods to compare multiple high-temperature indices associated with all-cause mortality and outpatient visits for population residing in a subtropical island. Apparent temperature is an optimal indicator for predicting all-cause mortality risk, and maximum temperature is recommended to associate with outpatient visits. The impact of heat varied with study areas, evaluated health outcomes, and high-temperature indices. The increased extreme heat is associated with stronger risk for all-cause mortality than for outpatient visits.
authors.affiliation: Environmental and Occupational Medicine and Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, 677 Huntington Ave., Boston, MA 02115, USA.
authors.forename: Yu-Kai
authors.initials: YK
authors.lastname: Lin
authors.forename: Chin-Kuo
authors.initials: CK
authors.lastname: Chang
authors.forename: Ming-Hsu
authors.initials: MH
authors.lastname: Li
authors.forename: Yu-Chung
authors.initials: YC
authors.lastname: Wu
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Wang
mesh_terms: D000553:Ambulatory Care / Q000706:statistics & numerical data; D055874:Extreme Heat / Q000009:adverse effects*; D018882:Heat Stress Disorders / Q000453:epidemiology* / Q000401:mortality; D006801:Humans; D008954:Models, Biological; D017711:Nonlinear Dynamics; D012306:Risk; D012621:Seasons; D013624:Taiwan / Q000453:epidemiology; D013997:Time Factors