PHWR Public Health Weekly Report

According to the “State of the Global Climate 2023” report, 2023 was the hottest year on record, with the global mean surface temperature (GMST) being 1.45℃ (uncertainty of ±0.12℃) higher than the pre-industrial level [1].

In 2023, several regions worldwide experienced severe heat waves. Some of the most severe and persistent ones occurred in southern Europe and North Africa, especially in the second half of July. Southeastern Europe experienced extreme heat at the end of July while Midwestern Europe faced heat waves in late August and early September [1]. Heat-related health risks are projected to increase due to global warming [2], and climate change is anticipated to have adverse health effects on public health [3].

According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, the GMST has already increased 1.09℃ since the pre-industrial level. Global warming is occurring faster than expected, and the global temperature is predicted to rise by 1.5℃ before 2040. In addition, the Earth’s temperature is expected to be approximately 3.2℃ higher than the pre-industrial level by 2100. A 0.5℃ rise in the Earth’s temperature due to global warming will increase mortality and morbidity rates, as well as result in labor productivity losses. Additionally, it will exacerbate the intensity and frequency of humid heat. If the global temperature rises by 2℃ by 2100, 18% of the existing plant and animal species will be at risk of extinction, and a 4℃ rise will threaten the survival of plants and animals as we know them every second. Importantly, animals that inhabit cold environments, such as those in alpine and polar regions, face a greater risk of becoming extinct [4].

The Republic of Korea has also experienced an increase in the number of days affected by heat waves, accompanied by an increase in the average temperature [5]. These environmental changes are increasing the frequency of heat-related illnesses, which pose a serious threat to human health. Heat-related illnesses occur when the body is exposed to excessive heat and include heat stroke, heat exhaustion, and heat cramps. These conditions can be life-threatening if not diagnosed and treated quickly. The Korea Disease Control and Prevention Agency (KDCA) has been operating the Heat-related Illness Surveillance Program since 2011, monitoring cases of heat-related illnesses and providing readily accessible reports on key case characteristics. This report analyze the key operational outcomes of the 2023 Heat-related Illness Surveillance Program and present the implications of the findings.

In 2023, 504 healthcare organizations and emergency departments (EDs) throughout the nation participated in the 2023 summer (May to September) Heat-related Illness Surveillance Program, which targeted patients who presented to an ED with a heat-related illness. Before any data were uploaded on the KDCA’s integrated disease health management system, they were first approved by designated public health centers, cities, and provinces and then given final approval by the KDCA. The information collected during operation of the program was posted on the KDCA’s website at 4:00 PM every day and was organized by period (daily and cumulative), region (province, city, county, and district), and key case characteristics.

This report analyzed the daily heat-related illness surveillance data from May 20 to September 30, 2023, by major case characteristics using Python 3.12.3.

Over the past 13 years (2011–2023), the annual average number of patients with heat-related illnesses reported through the surveillance program was 1,625, while the annual average number of deaths was 13.2. These values continue to climb every year (Figure 1) [6]. In 2023, 2,818 cases of heat-related illnesses were reported through the surveillance program, an increase of 80.2% from the previous year (1,564 in 2022), and a total of 32 deaths were presumed to be heat-related, representing an increase of 255.6% from the previous year (9 in 2022). Regarding major weather conditions in the summer of 2023, the number of days affected by heat waves was 14.2 days, an increase of 3.6 days since 2022 (10.6 days) (Table 1) [6]. As reported by the Korea Meteorological Administration, the national average temperatures in June, July, and August were 22.3℃, 25.2℃, and 26.4℃, which were 0.9℃, 0.9℃, and 1.3℃ higher, respectively. Thus, during summer (June–August), the national average temperature was 24.7℃, which was 1.0℃ higher than the 30-year average of 23.7℃. During the surveillance period (May 20–September 30), the number of heat-related illnesses peaked on August 3, 2023, with 133 cases. On August 3, the national average temperature was 34.1℃, with temperatures in Gangneung reaching 38.3℃ (Figure 2). Regarding the characteristics of patients with heat-related illnesses, the majority were male, with 2,192 reported cases (77.8%), and those in their 50s (21.3%). The number of heat-related illnesses per 100,000 people by age was 11.5 for those aged 80 years and older, with an increasing trend observed by age. In terms of region, Gyeonggi-do had the largest number of cases (i.e., 683, 24.2%), followed by Gyeongbuk (9.0%), Gyeongnam (8.0%), and Jeonnam (7.9%). The number of heat-related illnesses per 100,000 people by region was 14.5 in Jeju Island, 12.3 in Jeonnam, 11.8 in Jeonbuk, and 10.0 in Gyeongbuk. Regarding the type of illness, heat exhaustion accounted for 1,598 (56.7%) of the cases, followed by heat stroke (i.e., 493 cases, 17.5%). Of all the reported cases of heat-related illnesses, 79.6% occurred while those affected were engaged in outdoor activities. A closer look at outdoor occurrences revealed that individuals affected were often working, for example, in outdoor workshops (32.4%) and fields (14.0%) (Table 2).

Figure 1. Results of heat-related illness surveillance system operation and number of heat wave days by year
*p<0.01. Adapted from the article of Park et al. (Public Health Wkly Rep 2023;16:241-52) [6].

Figure 2. Current status of daily heat-related illness and average daily maximum temperature (℃) in the summer of 2023

Table 1 Results of surveillance system operation by year (2011–2023)

Year	Period of surveillance	Total casesa)	Deaths (n)	No. of days of heat waveb)
2011	July 1–Sept. 3	443	6	6.5
2012	June 1–Sept. 6	984	15	14.0
2013	June 2–Sept. 7	1,189	14	16.6
2014	June 1–Sept. 6	556	1	6.6
2015	May 24–Sept. 5	1,056	11	9.6
2016	May 23–Sept. 21	2,125	17	22.0
2017	May 29–Sept. 8	1,574	11	13.5
2018	May 20–Sept. 10	4,526	48	31.0
2019	May 20–Sept. 20	1,841	11	12.9
2020	May 20–Sept. 13	1,078	9	7.7
2021	May 20–Sept. 30	1,376	20	11.8
2022	May 20–Sept. 30	1,564	9	10.6
2023	May 20–Sept. 30	2,818	32	14.2

Sept=September. ^a)Total cases include death cases. ^b)Korea Meteorological Administration, Open MET Data Portal. Adapted from the article of Park et al. (Public Health Wkly Rep 2023;16:241-52) [6]..

Table 2 Main results of the 2023 heat-related illness surveillance system

Characteristic	HRI patients (%)
Sex
Male	2,192 (77.8)
Female	626 (22.2)
Age (yr)
0–9	16 (0.6)
10–19	95 (3.4)
20–29	291 (10.3)
30–39	323 (11.5)
40–49	385 (13.7)
50–59	601 (21.3)
60–69	514 (18.2)
70–79	325 (11.5)
≥80	268 (9.5)
Region
Seoul	201 (7.1)
Busan	94 (3.3)
Daegu	59 (2.1)
Incheon	113 (4.0)
Gwangju	64 (2.3)
Daejeon	41 (1.5)
Ulsan	68 (2.4)
Sejong	27 (1.0)
Gyeonggi	683 (24.2)
Gangwon	104 (3.7)
Chungbuk	151 (5.3)
Chungnam	205 (7.3)
Jeonbuk	207 (7.3)
Jeonnam	222 (7.9)
Gyeongbuk	255 (9.0)
Gyeongnam	226 (8.0)
Jeju	98 (3.5)
Diagnosis
Heatstroke	493 (17.5)
Heat exhaustion	1,598 (56.7)
Heat cramp	432 (15.3)
Heat syncope	235 (8.3)
Heat edema	1 (0.0)
Other effects of heat and light	59 (2.1)
Place of occurrence
Indoor	575 (20.4)
Home	171 (6.1)
Building	72 (2.6)
Workplace	197 (7.0)
Plastic greenhouse	48 (1.7)
Other	87 (3.1)
Outdoor	2,243 (79.6)
Workplace	913 (32.4)
Playground	171 (6.1)
Farmland	395 (14.0)
Mountain	72 (2.6)
Riverside	32 (1.1)
Roadside	286 (10.1)
Nearby residence	105 (3.7)
Other	269 (9.5)

HRI=heat-related illnesses..

Heat waves induced by climate change are becoming more frequent in many regions worldwide, resulting in a persistent annual increase in health-related consequences. Heat waves have a direct impact on society, including a decline in the labor force.

Heat-related illnesses occurring during the summer can be reduced or prevented with the adoption of simple health measures; failure to adhere to these recommendations can lead to casualties. For instance, when going out in the heat, bringing a hat or handheld parasol for sun protection is recommended, as is wearing loose-fitting clothing and drinking plenty of water, even before feeling thirsty. Working during the hottest times of the day should be avoided, and taking breaks is suggested. Older adults, pregnant women, and those with underlying medical conditions (e.g., cardiovascular disease, diabetes, and stroke) are especially vulnerable to heat-related illnesses due to decreased thermoregulation; therefore, they should closely adhere to heat-related illness prevention tips during heat waves while sticking to a daily healthcare routine [7].

To minimize the adverse effects of heat waves on health, the government is systematically implementing measures through relevant ministries and sectors. During the annual government-wide comprehensive planning period (May 20 to September 30), the KDCA will continue to operate the Heat-related Illness Surveillance Program to quickly identify health effects caused by heat waves. Throughout the program, collected data will be posted at 4:00 PM daily on the KDCA website (http://www.kdca.go.kr). When the program ends, the “Annals of Reported Heat-related Illnesses due to Heat Waves” will be published annually to serve as a basis for future heat wave response measures and policy establishment.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: None.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: DSA, YJA, JHL. Data curation: JHL. Formal analysis: JHL. Investigation: JHL. Methodology: JHL. Visualization: JHL. Writing – original draft: JHL. Writing – review & editing: DSA, YJA.