Jongsik Ha

Effect of Previous-Winter Mortality on the Association between Summer Temperature and Mortality in South Korea

Background It has recently been postulated that low mortality levels in the previous winter may increase the proportion of vulnerable individuals in the pool of people at risk of heat-related death during the summer months. Objectives We explored the sensitivity of heat-related mortality in summer (June–August) to mortality in the previous winter (December–February) in Seoul, Daegu, and Incheon in South Korea, from 1992 through 2007, excluding the summer of 1994. Methods Poisson regression models adapted for time-series data were used to estimate associations between a 1°C increase in average summer temperature (on the same day and the previous day) above thresholds specific for city, age, and cause of death, and daily mortality counts. Effects were estimated separately for summers preceded by winters with low and high mortality, with adjustment for secular trends. Results Temperatures above city-specific thresholds were associated with increased mortality in all three cities. Associations were stronger in summers preceded by winters with low versus high mortality levels for all nonaccidental deaths and, to a lesser extent, among persons ≥ 65 years of age. Effect modification by previous-winter mortality was not evident when we restricted deaths to cardiovascular disease outcomes in Seoul. Conclusions Our results suggest that low winter all-cause mortality leads to higher mortality during the next summer. Evidence of a relation between increased summer heat-related mortality and previous wintertime deaths has the potential to inform public health efforts to mitigate effects of hot weather.

Distributed lag effects in the relationship between temperature and mortality in three major cities in South Korea.

In many cases, the effect of an environmental exposure event is not restricted to the period when it occurs. Understanding the extent to which high-temperature exposure hastens the occurrence of health outcomes is a key to interpreting public health risks correctly and developing appropriate intervention programs related to heat. We explored distributed lag effects in the relationship between high temperature and mortality in summer (June-August) in Seoul, Daegu, and Incheon, South Korea, from 1991 to 2008. A Poisson regression model adapted for time-series data was used to estimate short-term heat-related mortality impacts. To examine the distributed lag effects, we fitted a constrained distributed lag model that included lagged exposure variables as covariates, applying a function of days of lag according to B-spline bases. The effects on mortality caused by high-temperature exposure continued for about 5 days, and slight deficit effects after the initial mortality increases were observed, even if not initially apparent. Thirty days after high-temperature exposure, the cumulative effects were still high in Seoul and Incheon. This study shows a pattern of distributed lag effects of high-temperature exposure that the single-day model could not identify. Our results confirm that summer high temperature has an effect on mortality, not advancing the date of adverse events by a few days. Ultimately, it suggests that public health programs be amended to allow for differential high-temperature effects spread over multiple days.

Relationship between winter temperature and mortality in Seoul, South Korea, from 1994 to 2006

In South Korea, the mortality increases with temperature above a certain threshold during the warm season. In contrast, despite the common burden of cold weather, little is known about the effects of low temperatures on mortality. We evaluated the relationship between low temperatures and mortality in winter (December-February) in Seoul, South Korea, from 1994 to 2006. Data were obtained from government agencies. After adjusting for trends in time, day of the week, holidays, and relative humidity, we explored the associations between mortality and various cold indicators of winter in Seoul, South Korea. First, we fitted nonparametric smoothing regression models to check the shape of associations and then fitted threshold models (including two different slopes in a model) to estimate the thresholds and the effects of low temperatures using the Akaike Information Criterion (AIC). The graphical associations between cardiorespiratory, cardiovascular, and all causes of mortality and the cold wave index (CWI=T(min, previous day)-T(min, current day)) were observed. We confirmed the threshold according to a lag structure and after that, estimated the effects of CWI below the threshold, respectively. The effects of the daytime CWI lagged by 0-2 days were the strongest among those of the daytime CWI lagged by 0-6 days. The most significant mortality outcomes were cardiovascular-related. Although we could not consider respiratory-related mortality, the effect of CWI on cardiovascular-related mortality below a certain threshold was greater than cardiorespiratory-related or all cause-related mortality. In addition, the association between mortality and CWI was more immediate and vulnerable in an elderly subgroup (> or =65 years old) than in a younger subgroup (0-64 years old). Our results suggest that public health programs should be considered to alleviate not only the effect of sudden change in winter temperature on mortality.

Implication of ultraviolet B radiation exposure for non-melanoma skin cancer in Korea

Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the two most common subtypes of non-melanoma skin cancer (NMSC). Ultraviolet B radiation (UVB) exposure has been correlated with the occurrence of NMSC in humans. Thus far, studies investigating UVB-associated risk factors for NMSC in Asia have not been completed. The goal of this study was to evaluate the impact of UVB radiation exposure on the incidence of NMSC. Using UVB index and National Health Insurance databases, we performed a regression analysis using a linear model to describe the relationship between UVB measurements and NMSC incidence. The cut-off age at which the number of NMSC patients increased significantly was 60 years old. Our study found that 52.2% of NMSC patients were males, while 47.8% were females. There was a strong positive correlation between the annual UVB index and NMSC incidence rates in individuals 60 years and older. Males, individuals 60 years and older and persons who live in higher UVB index in Korea might be susceptible to NMSC.

The weather watch/warning system for stroke and asthma in South Korea

Weather watch/warning systems have been established for human health outcomes. Our study aims to develop and demonstrate a weather watch/warning system for asthma and stroke within the whole of South Korea, using a stratified regression approach. We converted claim-based health insurance data covering almost all medical claims for the only health insurance system in Korea for asthma and stroke from 1996–2003 into personalized disease episode data, and combined them with meteorological data. We utilized a step-wise regression method using factors extracted from the meteorological data to develop stratified models for six (stroke) and nine (asthma) regional and day-of-week strata. Validation studies showed that the actual number of hospitalizations in 2003 increased according to the three-leveled predictions (levels I, II, and III) from the model based on the 1996–2002 data. This system is accessible via the internet (http://industry.kma.go.kr/APP/sub_APP15_H01.htm) at the Korean Meteorological Administration website.

Impacts of typhoon and heavy rain disasters on mortality and infectious diarrhea hospitalization in South Korea

Several studies for health impacts of natural disasters have not been comprehensive with respect to disaster type and areas, nor quantitative. The aim of our study is to quantitatively examine the associations between disasters and human health in South Korea. This study considered “special disasters” that occurred from 2003 to 2009 in seven metropolitan cities and nine provinces in South Korea. First, we completed health impact counts in both disaster periods and reference periods. We then calculated the rate ratios between health impact counts in these two periods. Mortality is estimated to be higher in the case of typhoons, whereas morbidity is estimated to be higher in heavy rain disasters. The difference in health impacts of typhoons and heavy rain may be explained by the difference in meteorological exposure patterns. Consequentially, we suggest the development of properly adaptive plans against the influence of future natural disasters on human health.

Utilization of health insurance data in an environmental epidemiology

Objectives In South Korea, health insurance data are used as material for the health insurance of national whole subject. In general, health insurance data could be useful for estimating prevalence or incidence rate that is representative of the actual value in a population. The purpose of this study was to apply the concept of episode of care (EoC) in the utilization of health insurance data in the field of environmental epidemiology and to propose an improved methodology through an uncertainty assessment of disease course and outcome. Methods In this study, we introduced the concept of EoC as a methodology to utilize health insurance data in the field of environmental epidemiology. The characterization analysis of the course and outcome of applying the EoC concept to health insurance data was performed through an uncertainty assessment. Results The EoC concept in this study was applied to heat stroke (International Classification of Disease, 10th revision, code T67). In the comparison of results between before and after applying the EoC concept, we observed a reduction in the deviation of daily claims after applying the EoC concept. After that, we categorized context, model, and input uncertainty and characterized these uncertainties in three dimensions by using uncertainty typology. Conclusions This study is the first to show the process of constructing episode data for environmental epidemiological studies by using health insurance data. Our results will help in obtaining representative results for the processing of health insurance data in environmental epidemiological research. Furthermore, these results could be used in the processing of health insurance data in the future.