Temperature-mortality Association Research Articles

Modification of Temperature-Mortality Association in Summer by the Previous Winter Mortality in South Korea

ISEE-0388 Background and Objective: Numerous studies in recent years have reported association between summer temperature and deaths in cities. However, in summer when a greater pool of vulnerable individuals leave, the heat-related mortality is little known. We aimed to explore how sensitive the heat-related mortality in summer is to mortality in the previous winter in 3 major cities, in South Korea. Methods: In the study period from 1992–2007, summer and winter were defined as June-August and December-February, respectively. The statistical analysis was conducted in two steps. First, to investigate thresholds of the temperature-mortality curves in summer, we fitted piecewise log-linear models using AIC for the model-fitting criteria. Second, to investigate dependency of heat-mortality effects above the threshold on previous winter mortality, we incorporated indicators of mortality in winter as effect modifiers in the first step model. Results: Estimated thresholds for ≥65 year old age group with two day (lag 0 and 1) mean temperature (27.4°C, 27.3°C and 23.2°C for Seoul, Daegu, and Incheon, respectively) were lower than those for all age groups (27.9°C, 28.1°C and 25.5°C, respectively). For summer mortality of all age group, a 1°C increment in temperature above the thresholds was associated with an increase of 10.57%, 8.55%, and 6.04% for low strata, 4.85%, 4.00%, and 2.63% for high strata of winter mortality in Seoul, Daegu, and Incheon, respectively (P-values for heterogeneity: 0.0081, 0.0142, and 0.0378, respectively). Those for ≥65 year old age group were 8.85%, 8.36%, and 3.88% for low strata, 7.75%, 5.14%, and 2.83% for high strata, respectively (P-values for heterogeneity: 0.5846, 0.0502, and 0.2651, respectively). Conclusion: Our results show that low mortality in winter leads to higher mortality in the following summer. It suggests that the yearly variation of heat effect in summer should be reconsidered in public health program, especially in heat warning system.

Ambient Temperature and Mortality: An International Study in Four Capital Cities of East Asia

ISEE-0258 Background and Objective: Extreme ambient temperature has been associated with increased daily mortality across the world. We describe the ambient temperature-mortality association for four capital cities in East Asia, Seoul, Beijing, Tokyo, and Taipei, and identify a threshold temperature for each city and the percent increase in mortality. Methods: We observed that threshold temperatures vary by latitude. We adapted generalized linear modeling with natural cubic splines (GLM+NS) to examine the association between daily mean apparent temperature and total mortality, as well as mortality due to respiratory and cardiovascular causes in a threshold model. We conducted a time-series analysis adjusting for day of the week and long-term time trend. The study period differed by city. Results: The threshold temperature for all seasons was estimated to be 30.1–33.5°C, 31.3–32.3°C, 29.4–30.8°C, and 25.2–31.5°C for Seoul, Beijing, Tokyo, and Taipei, respectively, on the same day. For the summer season, the threshold temperature was 33.2–34.2°C, 30.8–29.7°C, 31.5°C, and 30.7–31.5°C for Seoul, Beijing, Tokyo, and Taipei, respectively. For the mean daily apparent temperature increase of 1°C above the thresholds in Seoul, Tokyo, and Taipei, estimated percentage increases in daily total mortality were 2.7 (95% confidence interval (CI) = 2.2–3.1), 1.7 (95% CI = 1.5–2.0), and 4.3 (95% CI = 2.9–5.7), respectively. Beijing provided no total mortality counts. Estimated percentage increases were 2.7–10.5 for respiratory mortality, 1.1–9.3 for cardiovascular mortality in 4 cities. Conclusions: This study identified increased mortality due to exposure to elevated apparent temperature. The importance of effects of apparent temperature and city-specific threshold temperatures suggests that analyses of the impact of climate change should take regional differences into consideration.

Ambient temperature and mortality: An international study in four capital cities of East Asia

Extreme ambient temperature has been associated with increased daily mortality across the world. We describe the ambient temperature–mortality association for four capital cities in East Asia, Seoul, Beijing, Tokyo, and Taipei, and identify a threshold temperature for each city and the percent increase in mortality. We adapted generalized linear modeling with natural cubic splines (GLM + NS) to examine the association between daily mean apparent temperature (AT) and total mortality, as well as mortality due to respiratory (RD) and cardiovascular (CVD) causes in a threshold model. We conducted a time-series analysis adjusting for day of the week and long-term time trend. The study period differed by city. The threshold temperature for all seasons was estimated to be 30.1–33.5 °C, 31.3–32.3 °C, 29.4–30.8 °C, and 25.2°–31.5 °C for Seoul, Beijing, Tokyo, and Taipei, respectively, on the same day. For the mean daily AT increase of 1 °C above the thresholds in Seoul, Tokyo, and Taipei, estimated percentage increases in daily total mortality were 2.7 (95% confidence interval (CI) = 2.2–3.1), 1.7 (95% CI = 1.5–2.0), and 4.3 (95% CI = 2.9–5.7), respectively. Beijing provided no total mortality counts. Estimated percentage increases were 2.7–10.5 for RD mortality, 1.1–9.3 for CVD mortality in 4 cities. This study identified increased mortality due to exposure to elevated AT. The importance of effects of AT and city-specific threshold temperatures suggests that analyses of the impact of climate change should take regional differences into consideration.

High ambient temperature and mortality: a review of epidemiologic studies from 2001 to 2008

BackgroundThis review examines recent evidence on mortality from elevated ambient temperature for studies published from January 2001 to December 2008.MethodsPubMed was used to search for the following keywords: temperature, apparent temperature, heat, heat index, and mortality. The search was limited to the English language and epidemiologic studies. Studies that reported mortality counts or excess deaths following heat waves were excluded so that the focus remained on general ambient temperature and mortality in a variety of locations. Studies focusing on cold temperature effects were also excluded.ResultsThirty-six total studies were presented in three tables: 1) elevated ambient temperature and mortality; 2) air pollutants as confounders and/or effect modifiers of the elevated ambient temperature and mortality association; and 3) vulnerable subgroups of the elevated ambient temperature-mortality association. The evidence suggests that particulate matter with less than 10 um in aerodynamic diameter and ozone may confound the association, while ozone was an effect modifier in the warmer months in some locations. Nonetheless, the independent effect of temperature and mortality was withheld. Elevated temperature was associated with increased risk for those dying from cardiovascular, respiratory, cerebrovascular, and some specific cardiovascular diseases, such as ischemic heart disease, congestive heart failure, and myocardial infarction. Vulnerable subgroups also included: Black racial/ethnic group, women, those with lower socioeconomic status, and several age groups, particularly the elderly over 65 years of age as well as infants and young children.ConclusionMany of these outcomes and vulnerable subgroups have only been identified in recent studies and varied by location and study population. Thus, region-specific policies, especially in urban areas, are vital to the mitigation of heat-related deaths.

Summer Temperature-related Mortality

Several studies have described seasonal patterns of mortality, with rates higher in winter and lower in summer. Few researchers, however, have analyzed how the mortality rate in winter may influence the temperature-mortality association in the following summer. In the present paper, we addressed the question of whether the association between summer temperature and mortality among the elderly is modified by the previous winter mortality rate. We selected all deaths in Rome during 1987-2005 among persons 65 years old or older. We collected data on daily mean temperature and humidity. We estimated the effect of summer apparent temperature on mortality by using a time-series approach, and tested the effect modification based on the mortality rate during the preceding winter. The effect of summer apparent temperature on mortality was stronger in years characterized by low mortality in the previous winter (relative risk for days at 30 degrees C vs. days at 20 degrees C = 1.73 [95% confidence interval = 1.50-2.01]), as contrasted with years with medium (1.32 [1.25-1.41]) or high winter mortality (1.34 [1.17-1.55]). The percentages of attributable risks for summer heat were 28%, 18%, and 18% for years characterized by low, medium, or high winter mortality rates respectively. Low-mortality winters may inflate the pool of the elderly susceptible population at risk for dying from high temperature the following summer.

Temperature-Related Mortality by Season in Seoul, South Korea, From 1994 to 2005

ISEE-491 Objective: Heat-related mortality studies have been largely reported. In particular, the temperature thresholds that mortality risk begins to rise as the temperature increases or decreases were suggested in an USA study. However, these temperatures varied by location. In this study, we evaluated the shape of temperature-mortality associations in 4 seasons of Seoul and analyzed the effects of temperature on mortality, especially among the vulnerable people. Material and Methods: We obtained mortality and meteorological data between 1994 and 2005 from the governmental agencies. After adjusting for the time-trend, day of the week and holidays, relative humidity, and air pressure, we explored various aspects of the association between mortality and temperature by season in Seoul, Korea. First, we fitted nonparametric smoothing regression models with lagged temperature variables to check the associations and then fitted threshold models (including 2 different slopes in a model) to estimate the thresholds and the effects. These thresholds were estimated by the AIC criteria. Results: We evaluated the shape of the temperature-mortality association on the lag structure according to seasons. But, we could see the graphical associations between temperature and mortality only in summer. We confirmed the statistical significance of the effect above the threshold in summer. The threshold values with moving average temperature of current and lagged 1 day were estimated as 27.8°C for 65+, as 28.3°C for all-aged population, and as 29.2°C for 64−. Thresholds for cardiovascular mortality were estimated as 28.3°C, 28.4°C, and 29.3°C for 65+, all aged, and 64−, respectively. Estimated percent increases as 1°C temperature increase above the thresholds were, respectively, 13.3%, 13.0%, and 12.2% in total mortality, 20.1%, 17.4%, and 12.2% in cardiovascular mortality. In respiratory mortality, thresholds and percent increases were estimated as 26.3°C, 6.6% for all aged. Conclusions: According to our findings, we suggest that Korean public health programs to prevent temperature-related mortality should be targeted at the vulnerable groups particularly in summer contrary to other countries.

Temperature and mortality in 11 cities of the eastern United States.

Episodes of extremely hot or cold temperatures are associated with increased mortality. Time-series analyses show an association between temperature and mortality across a range of less extreme temperatures. In this paper, the authors describe the temperature-mortality association for 11 large eastern US cities in 1973-1994 by estimating the relative risks of mortality using log-linear regression analysis for time-series data and by exploring city characteristics associated with variations in this temperature-mortality relation. Current and recent days' temperatures were the weather components most strongly predictive of mortality, and mortality risk generally decreased as temperature increased from the coldest days to a certain threshold temperature, which varied by latitude, above which mortality risk increased as temperature increased. The authors also found a strong association of the temperature-mortality relation with latitude, with a greater effect of colder temperatures on mortality risk in more-southern cities and of warmer temperatures in more-northern cities. The percentage of households with air conditioners in the south and heaters in the north, which serve as indicators of socioeconomic status of the city population, also predicted weather-related mortality. The model developed in this analysis is potentially useful for projecting the consequences of climate-change scenarios and offering insights into susceptibility to the adverse effects of weather.

Epidemiological studies of acute ozone exposures and mortality.

Many, but not all, observational epidemiological studies of ozone (O(3)) air pollution have yielded significant associations between variations in daily ambient concentrations of this pollutant and a wide range of adverse health outcomes. We evaluate some past epidemiological studies that have assessed the short-term association of O(3) with mortality, and investigate one possible reason for variations in their O(3) effect estimate, i.e., differences in their approaches to the modeling of weather influences on mortality. For all of the total mortality-air pollution time-series studies considered, the combined analysis yielded a relative risk, RR=1.036 per 100-ppb increase in daily 1-h maximum O(3) (95% CI: 1.023-1.050). However, the subset of studies that specified the nonlinear nature of the temperature-mortality association yielded a combined estimate of RR=1.056 per 100 ppb (95% CI: 1.032-1.081). This indicates that past time-series studies using linear temperature-mortality specifications have underpredicted the premature mortality effects of O(3) air pollution. For Detroit, MI, an illustrative analysis of daily total mortality during 1985-1990 also indicated that the model weather specification choice can influence the O(3) health effects estimate. Results were intercompared for alternative weather specifications. Nonlinear specifications of temperature and relative humidity (RH) yielded lower intercorrelations with the O(3) coefficient, and larger O(3) RR estimates, than a base model employing a simple linear spline of hot and cold temperature. We conclude that, unlike for particulate matter (PM) mass, the mortality effect estimates derived by time-series analyses for O(3) can be sensitive to the way that weather is addressed in the model. The same may well also be true for other pollutants with largely temperature-dependent formation mechanisms, such as secondary aerosols. Generally, we find that the O(3)-mortality effect estimate increases in size and statistical significance when the nonlinearity and the humidity interaction of the temperature-health effect association are incorporated into the model weather specification. We recommend that a minimization of the intercorrelations of model coefficients be considered (along with other critical factors such as goodness of fit, autocorrelation, and overdispersion) when specifying such a model, especially when individual coefficients are to be interpreted for risk estimation.