PHWR Public Health Weekly Report

According to a report in 2018 by the National Institute of Meteorological Research on 100 years of climate change on the Korean Peninsula, temperatures have increased by 1.4°C over the past 30 years compared with those in the early 20th century (1912–1941). The length of the summer season has increased by 19 days from 98 to 117 days, whereas that of the winter season has decreased from 109 to 91 days [1]. 2024 was officially recognized as the hottest year in the 113-year observation history of the Republic of Korea [2], and the number of patients with heat-related illnesses reached 3,704, the second-highest level since the inception of the surveillance system in 2011 [3]. As global warming becomes a more prominent issue in public discourse, concerns regarding its deleterious consequences across various sectors are mounting. The agricultural sector anticipates an augmentation in the number of growing degree days, a modification in the period requiring heating and cooling, and an escalation in both total rainfall and drought intensity [4]. Moreover, adverse effects on health are expected, with increased stress owing to weather and a rise in the heatstroke risk index being the most salient examples [4].

As average annual temperatures have generally increased and summers have lengthened, an increase in the number of days with extreme heat and tropical nights has also been observed. Although certain indicators of extreme winter weather phenomena have decreased, others have increased. A comparison of cold days, cold night/days, freezing days, and frost days from 1998 to 2017 with those from 2008 to 2017 reveals that they have increased to some extent [1]. Furthermore, although winter temperatures have exhibited an upward trend over the past 50 years, as evidenced by changes in both the average winter and average minimum temperatures, sudden, intense cold snaps over brief periods continue to occur. The national average temperature from December 2024 to February 2025 was 0.4°C, which was comparable with the long-term average. However, in February, an average temperature of –0.5°C was observed, marking the lowest recorded temperature in the past decade. This was further compounded by two instances of cold snaps lasting more than a week [5]. The Korea Disease Control and Prevention Agency (KDCA) has operated an emergency room-based surveillance system for cold-related illnesses and associated deaths during the winter months since December 2013, emulating its approach to monitoring the level of health hazards caused by heatwaves [6]. The surveillance period spans a duration of 90 days and is conducted annually from December 1 to the end of February. During this period, approximately 400 patients are reported on average.

In this study, we aimed to analyze the trends in cold-related illness cases from 2019–2025, coinciding with the initiation of the cold-related illness surveillance system. This information is aimed at providing foundational data to facilitate the prevention of cold-related illnesses and deaths among patients and understanding the current status of patient occurrences in the Daegu and Gyeongbuk regions under the jurisdiction of the Gyeongbuk Regional Disease Response Center. Overall, we aim to share awareness of the problem with local governments and relevant agencies within the region. Moreover, this study can serve as a point of reference for establishing goals for improvement, key areas of focus, and management methods.

1. Data Source

In this study, we utilized the raw data provided by the KDCA’s Cold-Related Illness Emergency Department Surveillance System, focusing specifically on cases of cold-related illnesses. The surveillance system for cold-related illnesses through emergency rooms has been in operation since 2013. However, data up to February 2019 only provided regional differentiation based on the reporting criteria. Consequently, the analysis was limited to data from December 2019 onward, enabling the execution of metropolitan city-/province-level analysis based on the location of occurrence. As winter extends from December to February of the subsequent year, the concept of a year was delineated through seasons. In particular, the winter season spanning from December 1, 2019 to February, 2020 was designated as the 2019–2020 season. Data from six winter seasons, including the 2019–2020 season through the 2024–2025 season, were used.

Cold-related illnesses in this reporting system include hypothermia, frostbite, chilblains, immersion foot, and frostnip, as summarized in Supplementary Table 1 (available online).

2. Analytical Methods

Changes in the outbreak scale were analyzed separately by season; however, owing to the limited number of patients per city or province, such as Daegu and Gyeongbuk, analyses based on the time of occurrence, location, treatment outcomes, and disease type were conducted by combining all six seasons. The data provided three types of regional information: areas where cold-related illnesses occurred, patients’ residential regions, and reporting regions. In this study, we analyzed data based on the region of occurrence. The number of reported cases per 100,000 individuals was calculated using the resident registration population data for December in each season for analysis.

From the 2019–2020 through the 2024–2025 season, a total of 2,217 cases of cold-related illnesses occurred nationwide across six seasons, averaging 369.5 cases per season (minimum 300, maximum 447) (Table 1). During the 3-month period of operating the cold-related illness surveillance system, the lowest number of patients was observed in February, irrespective of the season, whereas comparatively higher numbers of patients were observed in December and January. The total number of patients with cold-related illnesses in Daegu was 43 across all six seasons, with an average of 7.2 per season (minimum 4, maximum 12). In Gyeongbuk, the total was 223, averaging 37.2 per season (minimum 22, maximum 44).

Table 1 Reported cases per 100,000 population of cold-related illness in Daegu and Gyeongbuk (2019–2025 season)

Cities and provinces/mo	2019–2020	2020–2021	2021–2022	2022–2023	2023–2024	2024–2025	Total of 6 seasons
Nationwide
Total	303	433	300	447	400	334	2,217
	(0.58)a)	(0.84)	(0.58)	(0.87)	(0.78)	(0.65)	(0.72)
December	127	141	112	177	163	114	834
	(0.25)	(0.27)	(0.22)	(0.34)	(0.32)	(0.22)	(0.27)
January	96	236	109	199	149	122	911
	(0.19)	(0.46)	(0.21)	(0.39)	(0.29)	(0.24)	(0.29)
February	80	56	79	71	88	98	472
	(0.15)	(0.11)	(0.15)	(0.14)	(0.17)	(0.19)	(0.15)
Daegu
Total	6	5	12	8	8	4	43
	(0.25)	(0.21)	(0.50)	(0.34)	(0.34)	(0.17)	(0.30)
December	4	2	4	4	4	-	18
	(0.17)	(0.08)	(0.17)	(0.17)	(0.17)	-	(0.13)
January	2	3	5	2	2	2	16
	(0.08)	(0.12)	(0.21)	(0.08)	(0.08)	(0.08)	(0.11)
February	-	-	3	2	2	2	9
	-	-	(0.13)	(0.08)	(0.08)	(0.08)	(0.06)
Gyeongbuk
Total	22	41	43	34	44	39	223
	(0.83)	(1.55)	(1.64)	(1.31)	(1.72)	(1.54)	(1.43)
December	11	18	12	14	15	15	85
	(0.42)	(0.68)	(0.46)	(0.54)	(0.59)	(0.59)	(0.55)
January	5	17	22	15	15	18	92
	(0.19)	(0.64)	(0.84)	(0.58)	(0.59)	(0.71)	(0.59)
February	6	6	9	5	14	6	46
	(0.23)	(0.23)	(0.34)	(0.19)	(0.55)	(0.24)	(0.30)

Values are presented as cases, cases per 100,000 population. ^a)Values in parentheses are reported cases per 100,000 population..

When all six seasons are analyzed together, the numbers of reported cases per 100,000 individuals nationwide were 0.72, with 0.99 and 0.44 cases for male and female, respectively, indicating a higher incidence among male than female (Table 2). The incidence was lowest among those in their thirties, excluding those under 10 years of age. The incidence increased with age, reaching a peak value of 7.53 cases per 100,000 individuals among those aged 90 years and above. The number of reported cases per 100,000 people in Daegu was 0.30, lower than the national average. Meanwhile, Gyeongbuk recorded 1.43 cases per 100,000 individuals, twice the national level. In Gyeongbuk, the incidence was also notably high in the older age groups, with 5.93 and 17.54 reported cases per 100,000 individuals aged 80–89 years and 90 years and older, respectively.

Table 2 Age distribution of patients with cold-related illness in Daegu and Gyeongbuk (merge of 2019–2025 season)

Cities and provinces	Nationwide				Daegu				Gyeongbuk
	Total	Male	Female		Total	Male	Female		Total	Male	Female
Total	2,217	1,527	690		43	34	9		223	136	87
	(0.72)a)	(0.99)	(0.44)		(0.30)	(0.48)	(0.12)		(1.43)	(1.73)	(1.13)
0–9 yr	24	17	7		-	-	-		-	-	-
	(0.11)	(0.15)	(0.07)		-	-	-		-	-	-
10–19 yr	117	92	25		4	3	1		9	8	1
	(0.41)	(0.63)	(0.18)		(0.30)	(0.44)	(0.16)		(0.68)	(1.15)	(0.16)
20–29 yr	177	138	39		1	1	-		11	10	1
	(0.46)	(0.68)	(0.21)		(0.06)	(0.10)	-		(0.69)	(1.11)	(0.15)
30–39 yr	134	103	31		1	1	-		5	3	2
	(0.33)	(0.49)	(0.16)		(0.06)	(0.11)	-		(0.30)	(0.34)	(0.26)
40–49 yr	175	131	44		5	3	2		18	12	6
	(0.36)	(0.53)	(0.18)		(0.23)	(0.28)	(0.18)		(0.81)	(1.04)	(0.57)
50–59 yr	343	282	61		9	9	-		41	35	6
	(0.66)	(1.08)	(0.24)		(0.36)	(0.73)	-		(1.51)	(2.49)	(0.46)
60–69 yr	392	326	66		7	6	1		38	28	10
	(0.90)	(1.53)	(0.30)		(0.34)	(0.60)	(0.09)		(1.46)	(2.15)	(0.77)
70–79 yr	302	188	114		8	6	2		27	17	10
	(1.31)	(1.79)	(0.91)		(0.72)	(1.23)	(0.32)		(1.81)	(2.50)	(1.23)
80–89 yr	421	212	209		5	3	2		51	20	31
	(3.69)	(5.16)	(2.86)		(0.95)	(1.60)	(0.59)		(5.93)	(6.96)	(5.41)
≥90 yr	132	38	94		3	2	1		23	3	20
	(7.53)	(9.55)	(6.93)		(4.37)	(12.89)	(1.88)		(17.54)	(11.07)	(19.23)

Values are presented as cases, cases per 100,000 population. ^a)Values in parentheses are reported cases per 100,000 population..

The highest incidence of cold-related illnesses on a nationwide scale occurred between 7:00 and 8:00 a.m., with the majority of cases occurring during morning. A decline in cases was observed as the day progressed. No noticeable difference was observed in the peak occurrence times across the various age groups (Figure 1). The numbers of patients reported in Daegu and Gyeongbuk were lower than the national total; therefore, they were grouped and analyzed in 3-hours intervals. On a national scale, the highest number of patients was recorded between 6:00 and 9:00 a.m. (19.1%), and the highest patient counts were concurrently observed in Daegu (20.9%) and Gyeongbuk (23.8%) during this time period (Table 3). Based on location, the outdoors accounted for 77.9% of cold-related illnesses nationwide. In particular, roadsides were the most common location for cold-related illnesses at 25.8%, followed by homes (15.7%) and residential areas (15.4%). A similar trend was observed in Daegu, where cases occurring on the roadside accounted for the highest proportion at 32.6%, followed by those at homes (20.9%) and residential areas (18.6%). Within Gyeongbuk, a high frequency of cases was observed in these three locations, whereas patients observed in proximity to rivers and beaches accounted for a relatively high percentage of 16.1%.

Figure 1. Distribution of patients with cold-related illness by time of onset (merge of 2019–2025 season)

Table 3 Distribution of patients with cold-related illness by time and place of onset (merge of 2019–2025 season)

Time and place	Nationwide			Daegu			Gyeongbuk
	Patient	Rate (%)		Patient	Rate (%)		Patient	Rate (%)
Total	2,217	100.0		43	100.0		223	100.0
By time
00–03 hr	246	11.1		7	16.3		25	11.2
03–06 hr	233	10.5		6	14.0		24	10.8
06–09 hr	423	19.1		9	20.9		53	23.8
09–12 hr	325	14.7		7	16.3		32	14.3
12–15 hr	230	10.4		3	7.0		23	10.3
15–18 hr	278	12.5		1	2.3		23	10.3
18–21 hr	270	12.2		7	16.3		24	10.8
21–24 hr	212	9.6		3	7.0		19	8.5
By place
Indoor	489	22.1		13	30.2		50	22.4
Home	348	15.7		9	20.9		43	19.3
Indoor workplace	15	0.7		-	-		-	-
Building	76	3.4		3	7.0		5	2.2
Indoor, others	50	2.3		1	2.3		2	0.9
Outdoor	1,728	77.9		30	69.8		173	77.6
Outdoor workplace	90	4.1		-	-		6	2.7
Field	65	2.9		1	2.3		11	4.9
Playground (park)	39	1.8		-	-		2	0.9
Near residential area	342	15.4		8	18.6		32	14.3
Roadside	571	25.8		14	32.6		45	20.2
Riverside, beach	185	8.3		-	-		36	16.1
Mountains	178	8.0		2	4.7		10	4.5
Skating rink	1	0.0		-	-		-	-
Ski resort	34	1.5		-	-		-	-
Outdoor, others	223	10.1		5	11.6		31	13.9

Based on the type of condition, hypothermia accounted for the highest percentage of patients nationwide at 75.8%, followed by superficial frostbite (Supplementary Table 2; available online). Approximately 90% of cases in Daegu and Gyeongbuk were hypothermia. With respect to the outcomes of treatment, nationally, the largest proportion was accounted for by patients discharged or those who left without authorization (56.8%), whereas those admitted or transferred constituted 41.0% of the total. The total number of deaths across the six seasons was 50 patients, accounting for 2.3% of the total sample (Supplementary Table 3; available online). In Daegu, 46.5% of patients were discharged, whereas 53.5% received follow-up care through hospitalization or transfer. In Gyeongbuk, 58.7% of patients were discharged or left without authorization, 39.0% were hospitalized or transferred, and 2.2% died.

Cold-related illnesses refer to conditions, such as hypothermia, frostbite, and chilblains, all of which are caused by prolonged exposure to low temperatures. The KDCA is responsible for monitoring the occurrence of cold-related illnesses during periods of cold waves, classifying them as climate-related health hazards, akin to its monitoring of heat-related illnesses during heatwaves. The primary rationale for the close observation and accelerated dissemination of climate-related diseases is to mitigate health damage by enhancing public awareness and promoting preventative measures through the expeditious exchange of information. Deaths from heat-related illnesses accounted for less than 1% of all patients in 2024, and approximately 75% of patients were reported to have been discharged [3]. Conversely, among patients who presented to the emergency room with cold-related illnesses, less than 60% were discharged, whereas approximately 40% required hospitalization or transfer, and approximately 2% died. The number of patients with heat-related illnesses is approximately 15-fold higher than that with cold-related illnesses, and the absolute number of deaths is also higher for heat-related illnesses. However, the findings of this study underscore the heightened risk of heat-related illnesses and deaths.

A comparison of reported cases per 100,000 individuals across 17 cities and provinces nationwide shows a relatively higher trend in provincial areas and lower trend in metropolitan areas [6]. In this study, we also found that the reported cases per 100,000 individuals in Daegu were lower than the national average, whereas those in Gyeongbuk were twice the national level, ranking second highest among provinces after Gangwon [6]. Although the monthly minimum temperatures in Gyeongbuk are not particularly low compared with the national average, the region has a large older-adult population. According to the 2024 resident registration population, the proportions of individuals aged 70 years and older were 12.9, 13.5, and 17.4% in the nation, Daegu, and Gyeongbuk, respectively [7]. Among age groups, the highest number of cold-related illnesses occurred in those aged 80 years and older. Furthermore, a pronounced upward trend was observed in reported cases per 100,000 individuals with increasing age, underscoring the significance of this health concern across diverse age groups. In addition to low temperatures, several other factors are associated with the risk of cold-related illnesses, such as the maintenance of appropriate indoor temperatures, use of cold-proof and waterproof gear, and limitation of outdoor activities. Therefore, reliance on temperature as the sole determinant of high-risk areas is inadequate. A multitude of factors have been identified as major contributors to an increased risk of cold-related illnesses. These factors include the income level, advanced age, presence of underlying medical conditions, and alcohol consumption [8]. Although age can be determined with a reasonable degree of accuracy, assessing a patient’s state of drinking or underlying diseases in the emergency room is often unfeasible owing to the patient’s level of consciousness or cooperation. Therefore, caution must be exercised when interpreting results based solely on the response of patients who do not represent the entire population.

The highest number of patients was observed between 6:00 and 9:00 a.m., with more cases reported in the morning than in the afternoon. Notably, this time period corresponds with lower temperatures. Furthermore, the occurrence time does not necessarily indicate exposure to cold during that specific period. Therefore, some patients exposed to the cold for extended periods overnight may have been found in the morning. When classified by the location of occurrence, heat-related illnesses were more frequently reported outdoors than indoors; however, cases occurring at home also accounted for a significant proportion, at 15.7%. According to an analysis of mobility big data (compiled using smartphone applications of individuals aged 20–60 years) from April to June, 2023, as reported by the Korea Research Institute for Human Settlements, individuals reported spending 10.3 hours out of 24 hours outside their homes [9]. This finding is consistent with the observation that the time spent at home is considerably longer than that spent outdoors.

Despite the heightened perception of warming and comparatively smaller scale of cold-related illnesses relative to cold-related illnesses resulting in less attention being paid to the former, the severity associated with cold-related illnesses necessitates the consideration of measures for their prevention and management. Despite the global rise in average temperatures and increase in the number of extreme heat days, extreme cold snaps still occur, and a notable decrease in cold-related illnesses has not been confirmed. Consequently, sustained vigilance is essential regarding the health hazards associated with cold weather. Heat-related illnesses occur most frequently during the hottest hours of the day, when people are most active. Community centers can be operated as shared cooling shelters with support for cooling costs. However, the prevalence of cold-related illnesses is particularly pronounced during periods of patient convalescence at home. This poses challenges in terms of effective treatment and management through shared facilities, emphasizing that this aspect must be considered. This issue is particularly salient in Gyeongbuk, where a significant number of patients are observed to be at home, in contrast to the national level. Thus, adequate indoor heating must be promoted, and effective support measures must be reviewed for households struggling with heating costs.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: None.

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

Author Contributions: Data curation: SHK. Formal analysis: SHK. Writing – original draft: YMS. Writing – review & editing: YMS, SHK.

Supplementary data are available online.