Public Health Weekly Report 2025; 18(1): 17-32
Published online December 6, 2024
https://doi.org/10.56786/PHWR.2025.18.1.2
© The Korea Disease Control and Prevention Agency
Myung-Jae Hwang 1, So Yeon Park 1
, Hyungjun Kim 1
, Se Jeong Yang 1
, Sungchan Yang 2
, Jin Seon Yang 1*
1Division of Infectious Disease Control, Department of Infectious Disease Policy, Korea Disease Control and Prevention Agency, Cheongju, Korea, 2Division of Infectious Disease Response, Capital Regional Center for Disease Control and Prevention, Korea Disease Control and Prevention Agency, Seoul, Korea
*Corresponding author: Jin Seon Yang, Tel: +82-43-719-7140, E-mail: jsyang99@korea.kr
This is an Open Access journal distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) which permits unrestricted distribution, and reproduction in any medium, provided the original work is properly cited.
The Korea Disease Control and Prevention Agency (KDCA) is strengthening its management system by conducting nationwide epidemiological investigations and risk assessments for water and foodborne diseases. In addition, the KDCA operates the “Enhanced Surveillance of Water and Foodborne Disease Outbreaks” during high-risk periods from May to September every year. In 2023, 600 outbreaks were reported, including 329 large-scale and 271 small-scale incidents. Most outbreaks occurred in April (59, 9.8%), February (56, 9.3%), and December (55, 9.2%), with no significant increase during summer. Outbreaks were most frequent in restaurants (275, 45.8%), educational facilities (217, 36.2%), and group-living facilities (41, 6.8%), in that order. Most outbreaks occurred in educational facilities in March and September, coinciding with school opening, with 42 (7.0%) in elementary schools and 38 (6.3%) in kindergartens. The presumed source of infection was mainly “unknown” (373, 62.2%), followed by “carriers” (human-to-human transmission, food service employees, etc. [84, 14.0%]). “Norovirus” was the most commonly suspected pathogen (204, 34.0%), followed by “unknown” (182, 30.3%) and “ Salmonella” (48, 8.0%). Notably, 76.5% of outbreaks suspected of “Norovirus” were presumed to involve human-to-human transmission. As a analysis of water and foodborne disease outbreak in 2023, to prevent the spread of these diseases, it is essential to maintain an annual surveillance system, provide ongoing education for managers and workers in educational facilities, and promote personal hygiene education. Additionally, establishing surveillance systems to block transmission routes based on infection source characteristics is critical.
Key words Waterborne diseases; Foodborne diseases; Outbreaks; Epidemiological investigation
Water and foodborne diseases cause gastrointestinal symptoms through the consumption of water or food contaminated with pathogenic microorganisms, with increased risk in summer.
In 2023, 600 outbreaks of water and foodborne disease were reported nationwide, predominantly in restaurants and educational facilities, with high incidence during school openings (March and September).
Continuous operation of surveillance systems is necessary. However, efforts are needed to improve the identification of the presumed infection source, as only 37.8% of outbreaks had a confirmed source.
Water and foodborne infectious diseases lead to gastrointestinal symptoms such as diarrhea, abdominal pain, vomiting, and fever, which result from the consumption of food or water contaminated with pathogenic microorganisms. According to the Infectious Disease Control and Prevention Act, the national notifiable infectious diseases encompass 17 types of bacteria, 7 types of viruses, and 4 types of protozoa, categorized as Class 2, Class 3, and Class 4 infectious diseases. Additionally, other infectious diseases include Kudoa septempunctata and enteroaggregative Escherichia coli infections [1].
Class 2 and Class 3 infectious diseases are subject to a mandatory surveillance system, necessitating the reporting of all suspected cases. In contrast, Class 4 infectious diseases are monitored through a sentinel surveillance system, where confirmed cases must be reported by designated surveillance institutions [1]. For Class 4 infectious diseases, if more than two individuals consume the same food (including drinking water) and simultaneously exhibit symptoms of intestinal infection, this is classified as an infectious disease outbreak and reported as a cluster case, prompting an epidemiological investigation [2].
Currently, five regional Centers for Disease Control and Prevention—located in the Seoul Metropolitan area, Chungcheong area, Honam area, Gyeongbuk area, and Gyeongnam area—are responsible for managing epidemiological investigations into water and foodborne infectious diseases reported through the Integrated Information System for Infectious Disease Control (formerly the Integrated Disease Health Management System). Meanwhile, the Korea Disease Control and Prevention Agency (KDCA) conducts investigations and analyzes the outbreak of water and foodborne infectious diseases at the national level. This investigation aimed to assess the nationwide outbreak occurrence of water and foodborne infectious diseases reported in 2023 through the Integrated Disease Health Management System and to discuss future key response directions.
Based on data concerning water and foodborne infectious disease outbreaks reported to the Integrated Disease Management System from January 1 to December 31, 2023, an analysis was conducted on outbreak occurrence by region, month, scale, and location. To calculate and visualize the incidence rate (measured per 100,000 population) by region, the 2023 resident registration central population data provided by the National Statistical Office (Korean Statistical Information Service, https://kosis.kr) was utilized. Following the calculation of the incidence rate (per 100,000 population) for cities, counties, and districts, the Statistical Geographic Information Service (https://sgis.kostat.go.kr) provided by Statistics Korea was employed to visualize the distribution of outbreak report rates by region.
Currently, epidemiological investigations of water and foodborne infectious disease outbreaks are conducted by the respective public health centers. Epidemiological investigation reports for small-scale outbreaks (<7 cases) are prepared by the respective city or province, while reports for large-scale outbreaks (≥7 cases) are reviewed and disseminated by the relevant regional Centers for Disease Control and Prevention. At this stage, the causative pathogens, sources of infection, and outbreak locations should be identified through statistical analyses of the data collected during the epidemiological investigations and laboratory tests, in accordance with the standards outlined in the water and foodborne infectious disease control guidelines (2024). Moreover, diagnostic criteria for pathogens are employed to confirm the presence of pathogens responsible for an outbreak. To ascertain the source of infection, the three factors for establishing epidemiological relevance—temporal contingency, statistical significance of the strength of relevance, and consistency with existing knowledge—must be considered. Thus, to identify the distribution of presumed causative pathogens, suspected sources of infection, and occurrence locations, this investigation analyzed the reported findings and evaluations of relevant investigation reports. All descriptive statistical analyses were conducted using Microsoft Office Excel 2021 (Microsoft).
From January 1 to December 31, 2023, a total of 600 water and foodborne infectious disease outbreaks were reported to the Integrated Disease Management System, affecting 12,698 cases (Table 1). Among these outbreaks, 329 (54.8%) were classified as large-scale, while 271 (45.2%) were classified as small-scale. The highest number of outbreaks was reported in Gyeonggi, with 116 outbreaks (19.3%), followed by Seoul with 73 outbreaks (12.2%), Busan with 60 outbreaks (10.0%), Gyeongnam with 55 outbreaks (9.2%), and Gangwon with 53 outbreaks (8.8%). In terms of incidence rates per 100,000 population, Gwangju reported the highest incidence rate at 70.6, followed by Gangwon at 44.6, Jeju at 36.6, Chungnam at 31.1, and Busan at 31.0.
Number of outbreaks | Proportion (%) | Number of cases | Incidence rate (per 100,000)a) | |
---|---|---|---|---|
Total | 600 | 100.0 | 12,698 | 24.7 |
Small scale (<7 cases) | 271 | 45.2 | 970 | - |
Large scale (≥7 cases) | 329 | 54.8 | 11,728 | - |
Region | ||||
Seoul | 73 | 12.2 | 2,362 | 25.2 |
Busan | 60 | 10.0 | 1,021 | 31.0 |
Daegu | 23 | 3.8 | 521 | 21.9 |
Incheon | 26 | 4.3 | 407 | 13.6 |
Gwangju | 16 | 2.7 | 1,002 | 70.6 |
Daejeon | 7 | 1.2 | 23 | 1.6 |
Ulsan | 12 | 2.0 | 210 | 19.0 |
Sejong | 4 | 0.7 | 29 | 7.5 |
Gyeonggi | 116 | 19.3 | 3,223 | 23.6 |
Gangwon | 53 | 8.8 | 681 | 44.6 |
Chungbuk | 21 | 3.5 | 342 | 21.5 |
Chungnam | 37 | 6.2 | 663 | 31.1 |
Jeonbuk | 17 | 2.8 | 327 | 18.6 |
Jeonnam | 21 | 3.5 | 455 | 25.2 |
Gyungbuk | 46 | 7.7 | 516 | 20.2 |
Gyungnam | 55 | 9.2 | 669 | 20.6 |
Jeju | 13 | 2.2 | 247 | 36.6 |
-=not available. a)Incidence rate=(No. of cases/No. of the resident registered population)×100,000.
Analysis of the incidence rate per 100,000 individuals by city, county, and district revealed that Haenam-gun in Jeollanam-do had the highest incidence rate at 305.7, followed by Uiwang-si in Gyeonggi-do at 284.5, Sunchang-gun in Jeollanam-do at 269.5, Taebaek-si in Gangwon-do at 222.9, and Hongcheon-gun in Gangwon-do at 222.0 (Figure 1).
By monthly, the highest number of outbreaks occurred in April, with 59 outbreaks (9.8%). This was followed by February with 56 outbreaks (9.3%), December with 55 outbreaks (9.2%), August with 54 outbreaks (9.0%), and January with 52 outbreaks (8.7%; Figure 2A). Meanwhile, the greatest number of patients affected by water and foodborne infectious diseases was observed in September, with 1,966 cases (15.5%), followed by July with 1,625 cases (12.8%), April with 1,276 cases (10.0%), and both August and December, each with 1,149 cases (9.0%; Figure 2B).
The analysis of outbreak locations by scale revealed that of the 275 outbreaks in restaurants, 75 (27.3%) were classified as large-scale and 200 (72.7%) as small-scale (Table 2). Additionally, among the 217 outbreaks related to educational and childcare facilities, there were 172 (79.3%) large-scale outbreaks and 45 (20.7%) small-scale outbreaks. Restaurants accounted for the most frequent outbreak locations, comprising 275 outbreaks (45.8%), followed by educational and childcare facilities with 217 outbreaks (36.2%), group living facilities with 41 outbreaks (6.8%), and workplaces as well as military, police, and firefighting facilities, each with 22 outbreaks (3.7%). Within the educational and childcare facilities, the data indicated that childcare centers experienced the highest number of outbreaks, totaling 89 (14.8%), followed by elementary schools with 42 outbreaks (7.0%) and kindergartens with 38 outbreaks (6.3%). Notably, when excluding outbreaks with “unknown” locations, large-scale outbreaks had the highest average number of cases per outbreak in “academy”—91.8 cases—indicative of high student concentration, followed by group facilities such as nursing homes, hospitals, and rehabilitation centers with an average of 63.0 cases, and funeral homes and wedding halls with 57.6 cases.
Location | Small scalea) | Large scalea) | Total | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | |||
Educational facilities | 45 | 207 | 4.6 | 20.7 | 172 | 4,882 | 28.4 | 79.3 | 217 | 5,089 | ||
Childcare center | 25 | 114 | 4.6 | 55.6 | 64 | 1,027 | 16.0 | 37.2 | 89 | 1,141 | ||
Kindergarten | 8 | 36 | 4.5 | 17.8 | 30 | 976 | 32.5 | 17.4 | 38 | 1,012 | ||
Elementary‧middle‧high school | 11 | 51 | 4.6 | 24.4 | 68 | 2,551 | 37.5 | 39.5 | 79 | 2,602 | ||
University, etc | 1 | 6 | 6.0 | 2.2 | 10 | 328 | 32.8 | 5.8 | 11 | 334 | ||
Workplace | 3 | 16 | 5.3 | 13.6 | 19 | 834 | 43.9 | 86.4 | 22 | 850 | ||
Home | 10 | 28 | 2.8 | 83.3 | 2 | 15 | 7.5 | 16.7 | 12 | 43 | ||
Funeral, wedding hall | 2 | 7 | 3.5 | 16.7 | 10 | 576 | 57.6 | 83.3 | 12 | 583 | ||
Academy | 1 | 4 | 4.0 | 20.0 | 4 | 367 | 91.8 | 80.0 | 5 | 371 | ||
Military‧police‧firefighting facilities | 1 | 2 | 2.0 | 4.5 | 21 | 643 | 30.6 | 95.5 | 22 | 645 | ||
Crowded facilitiesb) | 5 | 21 | 4.2 | 17.2 | 24 | 1,512 | 63.0 | 82.8 | 29 | 1,533 | ||
Restaurant | 200 | 669 | 3.3 | 72.7 | 75 | 2,576 | 34.3 | 27.3 | 275 | 3,245 | ||
Unknown | 4 | 16 | 4.0 | 66.7 | 2 | 323 | 161.5 | 33.3 | 6 | 339 |
a)Small scale was defined as less than seven cases in outbreak. Large scale was defined as more than seven cases in outbreak. b)Crowded facilities include nursing homes, hospitals, rehabilitation centers, and retreat centers, etc. c)Proportion was calculated by dividing by the total number of outbreaks (%).
Further analysis of outbreaks by location and time period revealed that 61.1% (33 outbreaks) of outbreaks in restaurants occurred in August, while 58.2% (32 outbreaks) of outbreaks in educational and childcare facilities took place in December (Figure 2).
In the event of an outbreak of a water and foodborne infectious disease, investigations are conducted to identify the presumed source of infection and the causative pathogens through epidemiological analysis. The results of these investigations (Figure 3) indicate that, out of a total of 600 outbreaks, the largest number had an “unknown” source of infection, comprising 373 outbreaks (62.2%). This was followed by outbreaks attributed to “carriers (e.g., human-to-human transmission, food service employees)” with 84 outbreaks (14.0%) and “other foods (e.g., mixed foods such as kimbap and budaejjigae)” with 36 outbreaks (6.0%). Regarding causative pathogens, “norovirus” was the most commonly identified, accounting for 204 outbreaks (34.0%), followed by “unknown” with 182 outbreaks (30.3%) and “Salmonella” with 48 outbreaks (8.0%). When examining causative pathogens based on presumed sources of infection—excluding cases where the source was “unknown”—it was found that in instances involving “carriers (e.g., human-to-human transmission, food service employees),” “norovirus” was identified as the source of infection in 92.8% of outbreaks. Conversely, for cases linked to “other foods (e.g., mixed foods such as kimbap and budaejjigae),” “Salmonella” represented the highest proportion, accounting for 33.3%. Notably, in cases where the presumed source of infection was identified as “eggs (eggs and egg products),” the causative pathogen was confirmed to be “Salmonella” in all instances.
From January 1 to December 31, 2023, a total of 600 water and foodborne infectious disease outbreaks were reported nationwide. While the timing of these outbreaks varied depending on whether the causative pathogen was viral or bacterial, they generally occurred throughout the year. In 2022, there were 86 outbreaks in July, 70 in June, and 58 in May, with relatively high occurrences in the summer months. In contrast, data from 2023 indicated no clear seasonal pattern in the monthly number of reported outbreaks (water and foodborne infectious disease control guidelines, 2024); however, there was an upward trend in the number of patients relative to the number of outbreaks.
The average number of cases per outbreak began to rise in June, when the average monthly temperature increased to 23.4°C (maximum temperature: 34.0°C). July recorded the highest number of patients, with 1,625 cases (compared to 1,031 cases in 2022) at an average temperature of 26.7°C (maximum temperature: 34.9°C). In September, the number of cases peaked 1,966 (compared to 749 in 2022), coinciding with an increase in the average maximum temperature to 32.8°C. Epidemiological investigations revealed that the majority of pathogens responsible for outbreaks during this period were identified as bacteria such as Salmonella, pathogenic Escherichia coli, and Campylobacter. These findings corroborate previous studies [3,4] that suggested a higher temperature and humid environment facilitate the proliferation of pathogenic bacteria, thereby escalating the risk of infectious disease transmission.
In educational and childcare facilities, there was a noticeable rise in water and foodborne infectious disease outbreaks in March and September, coinciding with the beginning of the school year. Notably, outbreaks were particularly prevalent in childcare centers (14.8% of total outbreaks), kindergartens (6.3%), and elementary schools (7.0%), where the population consists primarily of infants, toddlers, and young children. Although these facilities implement education and management protocols regarding personal hygiene to prevent infectious diseases, it is presumed that outbreaks continue to occur frequently due to the high population density, communal dining settings, and the heightened risk of disease transmission associated with shared facilities such as restrooms [4]. Therefore, childcare facilities that accommodate infants and young children must rigorously enforce both environmental hygiene management and educational programs focused on personal hygiene practices.
The proportion of outbreaks attributed to human-to-human transmission, excluding those with an “unknown” presumed source of infection, was found to be highest at 14%. This proportion may be influenced by human-to-human transmission being the primary route for norovirus transmission, especially given the rapid increase in norovirus infections in January 2023. Norovirus is primarily transmitted through the consumption of food contaminated with the virus present in stool and vomit [5,6]; however, human-to-human transmission is also recognized as a significant contributor to norovirus infections [7]. Generally, when determining the source of infection, if no association with food or water intake is established based on results from human and environmental specimen tests, the evaluation considers the incubation period of the pathogen, the movement of symptomatic patients, and the outbreak curve. If these factors indicate it is reasonable, the source is “presumed to be human-to-human transmission.” Therefore, to mitigate the risk of transmission through direct contact with an infected individual or indirect contact with contaminated objects, it is essential to adhere strictly to personal hygiene protocols and to disinfect affected environments [6].
The KDCA operates a “summer emergency quarantine system” aimed at intensively controlling and responding to the spread of water and foodborne infectious diseases during the peak season of outdoor activities (May to September) when food hygiene management is critical due to high temperatures and humidity. Nevertheless, to facilitate the monitoring and immediate response to related outbreaks throughout the year, we manage the spread of water and foodborne infectious diseases via this system. Analysis of outbreaks in 2023 highlighted the necessity of maintaining a surveillance system for water and foodborne infectious diseases, particularly to address outbreaks such as norovirus infections that may occur during colder seasons, in addition to those caused by bacteria in the summer.
Furthermore, to preemptively prevent large-scale outbreaks of water and foodborne infectious diseases, we are educating the public on adhering strictly to preventive measures. These measures include consuming safe water and food (such as cooking and boiling), washing hands with soap under running water for over 30 seconds, and refraining from cooking while experiencing diarrhea symptoms [4]. Additionally, we are promoting awareness of infectious disease prevention and compliance with hygiene standards among group meal managers and cooks working in educational and childcare facilities, where students and young children, who are particularly vulnerable to infection, are present.
Several limitations within the surveillance system for water and foodborne infectious disease outbreaks remain to be addressed.
First, the symptoms of water and foodborne infectious diseases are generally mild, such as vomiting and diarrhea. Consequently, if cases are not reported in a timely manner, the collection of samples and investigations into food and water intake histories may be delayed. This can hinder the identification of the presumed source of infection or the causative pathogen. In the analysis of presumed infection sources in 2023, 62.2% of outbreaks were classified as “unknown.” This is likely attributable to inadequate specimen acquisition related to delays in report submission during outbreaks, challenges in securing preserved food for epidemiological investigations, and low isolation rates of pathogens from both food and environmental samples. Therefore, it is essential to conduct ongoing education and public relations efforts to ensure that individuals exhibiting symptoms of enteric infections promptly report these symptoms to affiliated organizations or competent health institutions, facilitating effective epidemiological investigations.
Second, the results of epidemiological investigations, as reported by public health centers, are reviewed and disseminated by personnel in charge at regional disease response centers. However, differences in opinion may arise among these regional centers concerning the criteria set forth in the guidelines, such as the presumption of “human-to-human transmission,” when determining the source of infection. Thus, it is crucial to develop measures to address these discrepancies.
The surveillance system for water and foodborne infectious disease outbreaks serves as a proactive mechanism for curtailing the spread of such diseases within communities and for swiftly identifying sources of infection once an outbreak is recognized. To prevent large-scale outbreaks in the future, we are planning to implement campaigns and educational initiatives focused on prevention protocols, as well as to continue efforts aimed at enhancing the rate of infection source identification.
Ethics Statement: Not applicable.
Funding Source: None.
Acknowledgments: None.
Conflict of Interest: The authors have no conflicts of interest to declare.
Author Contributions: Conceptualization: MJH, SYP, HJK, SJY. Data curation: MJH, SCY, SJY. Formal analysis: MJH. Investigation: MJH, SYP, HJK, SJY. Methodology: MJH, SYP, HJK. Project administration: MJH, SYP. Resources: MJH, SCY, SJY. Supervision: JSY. Validation: SYP, HJK. Visualization: MJH, HJK. Writing – original draft: MJH, SYP. Writing – review & editing: SYP, JSY.
Public Health Weekly Report 2025; 18(1): 17-32
Published online January 2, 2025 https://doi.org/10.56786/PHWR.2025.18.1.2
Copyright © The Korea Disease Control and Prevention Agency.
Myung-Jae Hwang 1, So Yeon Park 1
, Hyungjun Kim 1
, Se Jeong Yang 1
, Sungchan Yang 2
, Jin Seon Yang 1*
1Division of Infectious Disease Control, Department of Infectious Disease Policy, Korea Disease Control and Prevention Agency, Cheongju, Korea, 2Division of Infectious Disease Response, Capital Regional Center for Disease Control and Prevention, Korea Disease Control and Prevention Agency, Seoul, Korea
Correspondence to:*Corresponding author: Jin Seon Yang, Tel: +82-43-719-7140, E-mail: jsyang99@korea.kr
This is an Open Access journal distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) which permits unrestricted distribution, and reproduction in any medium, provided the original work is properly cited.
The Korea Disease Control and Prevention Agency (KDCA) is strengthening its management system by conducting nationwide epidemiological investigations and risk assessments for water and foodborne diseases. In addition, the KDCA operates the “Enhanced Surveillance of Water and Foodborne Disease Outbreaks” during high-risk periods from May to September every year. In 2023, 600 outbreaks were reported, including 329 large-scale and 271 small-scale incidents. Most outbreaks occurred in April (59, 9.8%), February (56, 9.3%), and December (55, 9.2%), with no significant increase during summer. Outbreaks were most frequent in restaurants (275, 45.8%), educational facilities (217, 36.2%), and group-living facilities (41, 6.8%), in that order. Most outbreaks occurred in educational facilities in March and September, coinciding with school opening, with 42 (7.0%) in elementary schools and 38 (6.3%) in kindergartens. The presumed source of infection was mainly “unknown” (373, 62.2%), followed by “carriers” (human-to-human transmission, food service employees, etc. [84, 14.0%]). “Norovirus” was the most commonly suspected pathogen (204, 34.0%), followed by “unknown” (182, 30.3%) and “ Salmonella” (48, 8.0%). Notably, 76.5% of outbreaks suspected of “Norovirus” were presumed to involve human-to-human transmission. As a analysis of water and foodborne disease outbreak in 2023, to prevent the spread of these diseases, it is essential to maintain an annual surveillance system, provide ongoing education for managers and workers in educational facilities, and promote personal hygiene education. Additionally, establishing surveillance systems to block transmission routes based on infection source characteristics is critical.
Keywords: Waterborne diseases, Foodborne diseases, Outbreaks, Epidemiological investigation
Water and foodborne diseases cause gastrointestinal symptoms through the consumption of water or food contaminated with pathogenic microorganisms, with increased risk in summer.
In 2023, 600 outbreaks of water and foodborne disease were reported nationwide, predominantly in restaurants and educational facilities, with high incidence during school openings (March and September).
Continuous operation of surveillance systems is necessary. However, efforts are needed to improve the identification of the presumed infection source, as only 37.8% of outbreaks had a confirmed source.
Water and foodborne infectious diseases lead to gastrointestinal symptoms such as diarrhea, abdominal pain, vomiting, and fever, which result from the consumption of food or water contaminated with pathogenic microorganisms. According to the Infectious Disease Control and Prevention Act, the national notifiable infectious diseases encompass 17 types of bacteria, 7 types of viruses, and 4 types of protozoa, categorized as Class 2, Class 3, and Class 4 infectious diseases. Additionally, other infectious diseases include Kudoa septempunctata and enteroaggregative Escherichia coli infections [1].
Class 2 and Class 3 infectious diseases are subject to a mandatory surveillance system, necessitating the reporting of all suspected cases. In contrast, Class 4 infectious diseases are monitored through a sentinel surveillance system, where confirmed cases must be reported by designated surveillance institutions [1]. For Class 4 infectious diseases, if more than two individuals consume the same food (including drinking water) and simultaneously exhibit symptoms of intestinal infection, this is classified as an infectious disease outbreak and reported as a cluster case, prompting an epidemiological investigation [2].
Currently, five regional Centers for Disease Control and Prevention—located in the Seoul Metropolitan area, Chungcheong area, Honam area, Gyeongbuk area, and Gyeongnam area—are responsible for managing epidemiological investigations into water and foodborne infectious diseases reported through the Integrated Information System for Infectious Disease Control (formerly the Integrated Disease Health Management System). Meanwhile, the Korea Disease Control and Prevention Agency (KDCA) conducts investigations and analyzes the outbreak of water and foodborne infectious diseases at the national level. This investigation aimed to assess the nationwide outbreak occurrence of water and foodborne infectious diseases reported in 2023 through the Integrated Disease Health Management System and to discuss future key response directions.
Based on data concerning water and foodborne infectious disease outbreaks reported to the Integrated Disease Management System from January 1 to December 31, 2023, an analysis was conducted on outbreak occurrence by region, month, scale, and location. To calculate and visualize the incidence rate (measured per 100,000 population) by region, the 2023 resident registration central population data provided by the National Statistical Office (Korean Statistical Information Service, https://kosis.kr) was utilized. Following the calculation of the incidence rate (per 100,000 population) for cities, counties, and districts, the Statistical Geographic Information Service (https://sgis.kostat.go.kr) provided by Statistics Korea was employed to visualize the distribution of outbreak report rates by region.
Currently, epidemiological investigations of water and foodborne infectious disease outbreaks are conducted by the respective public health centers. Epidemiological investigation reports for small-scale outbreaks (<7 cases) are prepared by the respective city or province, while reports for large-scale outbreaks (≥7 cases) are reviewed and disseminated by the relevant regional Centers for Disease Control and Prevention. At this stage, the causative pathogens, sources of infection, and outbreak locations should be identified through statistical analyses of the data collected during the epidemiological investigations and laboratory tests, in accordance with the standards outlined in the water and foodborne infectious disease control guidelines (2024). Moreover, diagnostic criteria for pathogens are employed to confirm the presence of pathogens responsible for an outbreak. To ascertain the source of infection, the three factors for establishing epidemiological relevance—temporal contingency, statistical significance of the strength of relevance, and consistency with existing knowledge—must be considered. Thus, to identify the distribution of presumed causative pathogens, suspected sources of infection, and occurrence locations, this investigation analyzed the reported findings and evaluations of relevant investigation reports. All descriptive statistical analyses were conducted using Microsoft Office Excel 2021 (Microsoft).
From January 1 to December 31, 2023, a total of 600 water and foodborne infectious disease outbreaks were reported to the Integrated Disease Management System, affecting 12,698 cases (Table 1). Among these outbreaks, 329 (54.8%) were classified as large-scale, while 271 (45.2%) were classified as small-scale. The highest number of outbreaks was reported in Gyeonggi, with 116 outbreaks (19.3%), followed by Seoul with 73 outbreaks (12.2%), Busan with 60 outbreaks (10.0%), Gyeongnam with 55 outbreaks (9.2%), and Gangwon with 53 outbreaks (8.8%). In terms of incidence rates per 100,000 population, Gwangju reported the highest incidence rate at 70.6, followed by Gangwon at 44.6, Jeju at 36.6, Chungnam at 31.1, and Busan at 31.0.
Number of outbreaks | Proportion (%) | Number of cases | Incidence rate (per 100,000)a) | |
---|---|---|---|---|
Total | 600 | 100.0 | 12,698 | 24.7 |
Small scale (<7 cases) | 271 | 45.2 | 970 | - |
Large scale (≥7 cases) | 329 | 54.8 | 11,728 | - |
Region | ||||
Seoul | 73 | 12.2 | 2,362 | 25.2 |
Busan | 60 | 10.0 | 1,021 | 31.0 |
Daegu | 23 | 3.8 | 521 | 21.9 |
Incheon | 26 | 4.3 | 407 | 13.6 |
Gwangju | 16 | 2.7 | 1,002 | 70.6 |
Daejeon | 7 | 1.2 | 23 | 1.6 |
Ulsan | 12 | 2.0 | 210 | 19.0 |
Sejong | 4 | 0.7 | 29 | 7.5 |
Gyeonggi | 116 | 19.3 | 3,223 | 23.6 |
Gangwon | 53 | 8.8 | 681 | 44.6 |
Chungbuk | 21 | 3.5 | 342 | 21.5 |
Chungnam | 37 | 6.2 | 663 | 31.1 |
Jeonbuk | 17 | 2.8 | 327 | 18.6 |
Jeonnam | 21 | 3.5 | 455 | 25.2 |
Gyungbuk | 46 | 7.7 | 516 | 20.2 |
Gyungnam | 55 | 9.2 | 669 | 20.6 |
Jeju | 13 | 2.2 | 247 | 36.6 |
-=not available. a)Incidence rate=(No. of cases/No. of the resident registered population)×100,000..
Analysis of the incidence rate per 100,000 individuals by city, county, and district revealed that Haenam-gun in Jeollanam-do had the highest incidence rate at 305.7, followed by Uiwang-si in Gyeonggi-do at 284.5, Sunchang-gun in Jeollanam-do at 269.5, Taebaek-si in Gangwon-do at 222.9, and Hongcheon-gun in Gangwon-do at 222.0 (Figure 1).
By monthly, the highest number of outbreaks occurred in April, with 59 outbreaks (9.8%). This was followed by February with 56 outbreaks (9.3%), December with 55 outbreaks (9.2%), August with 54 outbreaks (9.0%), and January with 52 outbreaks (8.7%; Figure 2A). Meanwhile, the greatest number of patients affected by water and foodborne infectious diseases was observed in September, with 1,966 cases (15.5%), followed by July with 1,625 cases (12.8%), April with 1,276 cases (10.0%), and both August and December, each with 1,149 cases (9.0%; Figure 2B).
The analysis of outbreak locations by scale revealed that of the 275 outbreaks in restaurants, 75 (27.3%) were classified as large-scale and 200 (72.7%) as small-scale (Table 2). Additionally, among the 217 outbreaks related to educational and childcare facilities, there were 172 (79.3%) large-scale outbreaks and 45 (20.7%) small-scale outbreaks. Restaurants accounted for the most frequent outbreak locations, comprising 275 outbreaks (45.8%), followed by educational and childcare facilities with 217 outbreaks (36.2%), group living facilities with 41 outbreaks (6.8%), and workplaces as well as military, police, and firefighting facilities, each with 22 outbreaks (3.7%). Within the educational and childcare facilities, the data indicated that childcare centers experienced the highest number of outbreaks, totaling 89 (14.8%), followed by elementary schools with 42 outbreaks (7.0%) and kindergartens with 38 outbreaks (6.3%). Notably, when excluding outbreaks with “unknown” locations, large-scale outbreaks had the highest average number of cases per outbreak in “academy”—91.8 cases—indicative of high student concentration, followed by group facilities such as nursing homes, hospitals, and rehabilitation centers with an average of 63.0 cases, and funeral homes and wedding halls with 57.6 cases.
Location | Small scalea) | Large scalea) | Total | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | |||
Educational facilities | 45 | 207 | 4.6 | 20.7 | 172 | 4,882 | 28.4 | 79.3 | 217 | 5,089 | ||
Childcare center | 25 | 114 | 4.6 | 55.6 | 64 | 1,027 | 16.0 | 37.2 | 89 | 1,141 | ||
Kindergarten | 8 | 36 | 4.5 | 17.8 | 30 | 976 | 32.5 | 17.4 | 38 | 1,012 | ||
Elementary‧middle‧high school | 11 | 51 | 4.6 | 24.4 | 68 | 2,551 | 37.5 | 39.5 | 79 | 2,602 | ||
University, etc | 1 | 6 | 6.0 | 2.2 | 10 | 328 | 32.8 | 5.8 | 11 | 334 | ||
Workplace | 3 | 16 | 5.3 | 13.6 | 19 | 834 | 43.9 | 86.4 | 22 | 850 | ||
Home | 10 | 28 | 2.8 | 83.3 | 2 | 15 | 7.5 | 16.7 | 12 | 43 | ||
Funeral, wedding hall | 2 | 7 | 3.5 | 16.7 | 10 | 576 | 57.6 | 83.3 | 12 | 583 | ||
Academy | 1 | 4 | 4.0 | 20.0 | 4 | 367 | 91.8 | 80.0 | 5 | 371 | ||
Military‧police‧firefighting facilities | 1 | 2 | 2.0 | 4.5 | 21 | 643 | 30.6 | 95.5 | 22 | 645 | ||
Crowded facilitiesb) | 5 | 21 | 4.2 | 17.2 | 24 | 1,512 | 63.0 | 82.8 | 29 | 1,533 | ||
Restaurant | 200 | 669 | 3.3 | 72.7 | 75 | 2,576 | 34.3 | 27.3 | 275 | 3,245 | ||
Unknown | 4 | 16 | 4.0 | 66.7 | 2 | 323 | 161.5 | 33.3 | 6 | 339 |
a)Small scale was defined as less than seven cases in outbreak. Large scale was defined as more than seven cases in outbreak. b)Crowded facilities include nursing homes, hospitals, rehabilitation centers, and retreat centers, etc. c)Proportion was calculated by dividing by the total number of outbreaks (%)..
Further analysis of outbreaks by location and time period revealed that 61.1% (33 outbreaks) of outbreaks in restaurants occurred in August, while 58.2% (32 outbreaks) of outbreaks in educational and childcare facilities took place in December (Figure 2).
In the event of an outbreak of a water and foodborne infectious disease, investigations are conducted to identify the presumed source of infection and the causative pathogens through epidemiological analysis. The results of these investigations (Figure 3) indicate that, out of a total of 600 outbreaks, the largest number had an “unknown” source of infection, comprising 373 outbreaks (62.2%). This was followed by outbreaks attributed to “carriers (e.g., human-to-human transmission, food service employees)” with 84 outbreaks (14.0%) and “other foods (e.g., mixed foods such as kimbap and budaejjigae)” with 36 outbreaks (6.0%). Regarding causative pathogens, “norovirus” was the most commonly identified, accounting for 204 outbreaks (34.0%), followed by “unknown” with 182 outbreaks (30.3%) and “Salmonella” with 48 outbreaks (8.0%). When examining causative pathogens based on presumed sources of infection—excluding cases where the source was “unknown”—it was found that in instances involving “carriers (e.g., human-to-human transmission, food service employees),” “norovirus” was identified as the source of infection in 92.8% of outbreaks. Conversely, for cases linked to “other foods (e.g., mixed foods such as kimbap and budaejjigae),” “Salmonella” represented the highest proportion, accounting for 33.3%. Notably, in cases where the presumed source of infection was identified as “eggs (eggs and egg products),” the causative pathogen was confirmed to be “Salmonella” in all instances.
From January 1 to December 31, 2023, a total of 600 water and foodborne infectious disease outbreaks were reported nationwide. While the timing of these outbreaks varied depending on whether the causative pathogen was viral or bacterial, they generally occurred throughout the year. In 2022, there were 86 outbreaks in July, 70 in June, and 58 in May, with relatively high occurrences in the summer months. In contrast, data from 2023 indicated no clear seasonal pattern in the monthly number of reported outbreaks (water and foodborne infectious disease control guidelines, 2024); however, there was an upward trend in the number of patients relative to the number of outbreaks.
The average number of cases per outbreak began to rise in June, when the average monthly temperature increased to 23.4°C (maximum temperature: 34.0°C). July recorded the highest number of patients, with 1,625 cases (compared to 1,031 cases in 2022) at an average temperature of 26.7°C (maximum temperature: 34.9°C). In September, the number of cases peaked 1,966 (compared to 749 in 2022), coinciding with an increase in the average maximum temperature to 32.8°C. Epidemiological investigations revealed that the majority of pathogens responsible for outbreaks during this period were identified as bacteria such as Salmonella, pathogenic Escherichia coli, and Campylobacter. These findings corroborate previous studies [3,4] that suggested a higher temperature and humid environment facilitate the proliferation of pathogenic bacteria, thereby escalating the risk of infectious disease transmission.
In educational and childcare facilities, there was a noticeable rise in water and foodborne infectious disease outbreaks in March and September, coinciding with the beginning of the school year. Notably, outbreaks were particularly prevalent in childcare centers (14.8% of total outbreaks), kindergartens (6.3%), and elementary schools (7.0%), where the population consists primarily of infants, toddlers, and young children. Although these facilities implement education and management protocols regarding personal hygiene to prevent infectious diseases, it is presumed that outbreaks continue to occur frequently due to the high population density, communal dining settings, and the heightened risk of disease transmission associated with shared facilities such as restrooms [4]. Therefore, childcare facilities that accommodate infants and young children must rigorously enforce both environmental hygiene management and educational programs focused on personal hygiene practices.
The proportion of outbreaks attributed to human-to-human transmission, excluding those with an “unknown” presumed source of infection, was found to be highest at 14%. This proportion may be influenced by human-to-human transmission being the primary route for norovirus transmission, especially given the rapid increase in norovirus infections in January 2023. Norovirus is primarily transmitted through the consumption of food contaminated with the virus present in stool and vomit [5,6]; however, human-to-human transmission is also recognized as a significant contributor to norovirus infections [7]. Generally, when determining the source of infection, if no association with food or water intake is established based on results from human and environmental specimen tests, the evaluation considers the incubation period of the pathogen, the movement of symptomatic patients, and the outbreak curve. If these factors indicate it is reasonable, the source is “presumed to be human-to-human transmission.” Therefore, to mitigate the risk of transmission through direct contact with an infected individual or indirect contact with contaminated objects, it is essential to adhere strictly to personal hygiene protocols and to disinfect affected environments [6].
The KDCA operates a “summer emergency quarantine system” aimed at intensively controlling and responding to the spread of water and foodborne infectious diseases during the peak season of outdoor activities (May to September) when food hygiene management is critical due to high temperatures and humidity. Nevertheless, to facilitate the monitoring and immediate response to related outbreaks throughout the year, we manage the spread of water and foodborne infectious diseases via this system. Analysis of outbreaks in 2023 highlighted the necessity of maintaining a surveillance system for water and foodborne infectious diseases, particularly to address outbreaks such as norovirus infections that may occur during colder seasons, in addition to those caused by bacteria in the summer.
Furthermore, to preemptively prevent large-scale outbreaks of water and foodborne infectious diseases, we are educating the public on adhering strictly to preventive measures. These measures include consuming safe water and food (such as cooking and boiling), washing hands with soap under running water for over 30 seconds, and refraining from cooking while experiencing diarrhea symptoms [4]. Additionally, we are promoting awareness of infectious disease prevention and compliance with hygiene standards among group meal managers and cooks working in educational and childcare facilities, where students and young children, who are particularly vulnerable to infection, are present.
Several limitations within the surveillance system for water and foodborne infectious disease outbreaks remain to be addressed.
First, the symptoms of water and foodborne infectious diseases are generally mild, such as vomiting and diarrhea. Consequently, if cases are not reported in a timely manner, the collection of samples and investigations into food and water intake histories may be delayed. This can hinder the identification of the presumed source of infection or the causative pathogen. In the analysis of presumed infection sources in 2023, 62.2% of outbreaks were classified as “unknown.” This is likely attributable to inadequate specimen acquisition related to delays in report submission during outbreaks, challenges in securing preserved food for epidemiological investigations, and low isolation rates of pathogens from both food and environmental samples. Therefore, it is essential to conduct ongoing education and public relations efforts to ensure that individuals exhibiting symptoms of enteric infections promptly report these symptoms to affiliated organizations or competent health institutions, facilitating effective epidemiological investigations.
Second, the results of epidemiological investigations, as reported by public health centers, are reviewed and disseminated by personnel in charge at regional disease response centers. However, differences in opinion may arise among these regional centers concerning the criteria set forth in the guidelines, such as the presumption of “human-to-human transmission,” when determining the source of infection. Thus, it is crucial to develop measures to address these discrepancies.
The surveillance system for water and foodborne infectious disease outbreaks serves as a proactive mechanism for curtailing the spread of such diseases within communities and for swiftly identifying sources of infection once an outbreak is recognized. To prevent large-scale outbreaks in the future, we are planning to implement campaigns and educational initiatives focused on prevention protocols, as well as to continue efforts aimed at enhancing the rate of infection source identification.
Ethics Statement: Not applicable.
Funding Source: None.
Acknowledgments: None.
Conflict of Interest: The authors have no conflicts of interest to declare.
Author Contributions: Conceptualization: MJH, SYP, HJK, SJY. Data curation: MJH, SCY, SJY. Formal analysis: MJH. Investigation: MJH, SYP, HJK, SJY. Methodology: MJH, SYP, HJK. Project administration: MJH, SYP. Resources: MJH, SCY, SJY. Supervision: JSY. Validation: SYP, HJK. Visualization: MJH, HJK. Writing – original draft: MJH, SYP. Writing – review & editing: SYP, JSY.
Number of outbreaks | Proportion (%) | Number of cases | Incidence rate (per 100,000)a) | |
---|---|---|---|---|
Total | 600 | 100.0 | 12,698 | 24.7 |
Small scale (<7 cases) | 271 | 45.2 | 970 | - |
Large scale (≥7 cases) | 329 | 54.8 | 11,728 | - |
Region | ||||
Seoul | 73 | 12.2 | 2,362 | 25.2 |
Busan | 60 | 10.0 | 1,021 | 31.0 |
Daegu | 23 | 3.8 | 521 | 21.9 |
Incheon | 26 | 4.3 | 407 | 13.6 |
Gwangju | 16 | 2.7 | 1,002 | 70.6 |
Daejeon | 7 | 1.2 | 23 | 1.6 |
Ulsan | 12 | 2.0 | 210 | 19.0 |
Sejong | 4 | 0.7 | 29 | 7.5 |
Gyeonggi | 116 | 19.3 | 3,223 | 23.6 |
Gangwon | 53 | 8.8 | 681 | 44.6 |
Chungbuk | 21 | 3.5 | 342 | 21.5 |
Chungnam | 37 | 6.2 | 663 | 31.1 |
Jeonbuk | 17 | 2.8 | 327 | 18.6 |
Jeonnam | 21 | 3.5 | 455 | 25.2 |
Gyungbuk | 46 | 7.7 | 516 | 20.2 |
Gyungnam | 55 | 9.2 | 669 | 20.6 |
Jeju | 13 | 2.2 | 247 | 36.6 |
-=not available. a)Incidence rate=(No. of cases/No. of the resident registered population)×100,000..
Location | Small scalea) | Large scalea) | Total | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | Number of cases per 1 outbreak | Proportion (%)c) | Number of outbreaks | Number of cases | |||
Educational facilities | 45 | 207 | 4.6 | 20.7 | 172 | 4,882 | 28.4 | 79.3 | 217 | 5,089 | ||
Childcare center | 25 | 114 | 4.6 | 55.6 | 64 | 1,027 | 16.0 | 37.2 | 89 | 1,141 | ||
Kindergarten | 8 | 36 | 4.5 | 17.8 | 30 | 976 | 32.5 | 17.4 | 38 | 1,012 | ||
Elementary‧middle‧high school | 11 | 51 | 4.6 | 24.4 | 68 | 2,551 | 37.5 | 39.5 | 79 | 2,602 | ||
University, etc | 1 | 6 | 6.0 | 2.2 | 10 | 328 | 32.8 | 5.8 | 11 | 334 | ||
Workplace | 3 | 16 | 5.3 | 13.6 | 19 | 834 | 43.9 | 86.4 | 22 | 850 | ||
Home | 10 | 28 | 2.8 | 83.3 | 2 | 15 | 7.5 | 16.7 | 12 | 43 | ||
Funeral, wedding hall | 2 | 7 | 3.5 | 16.7 | 10 | 576 | 57.6 | 83.3 | 12 | 583 | ||
Academy | 1 | 4 | 4.0 | 20.0 | 4 | 367 | 91.8 | 80.0 | 5 | 371 | ||
Military‧police‧firefighting facilities | 1 | 2 | 2.0 | 4.5 | 21 | 643 | 30.6 | 95.5 | 22 | 645 | ||
Crowded facilitiesb) | 5 | 21 | 4.2 | 17.2 | 24 | 1,512 | 63.0 | 82.8 | 29 | 1,533 | ||
Restaurant | 200 | 669 | 3.3 | 72.7 | 75 | 2,576 | 34.3 | 27.3 | 275 | 3,245 | ||
Unknown | 4 | 16 | 4.0 | 66.7 | 2 | 323 | 161.5 | 33.3 | 6 | 339 |
a)Small scale was defined as less than seven cases in outbreak. Large scale was defined as more than seven cases in outbreak. b)Crowded facilities include nursing homes, hospitals, rehabilitation centers, and retreat centers, etc. c)Proportion was calculated by dividing by the total number of outbreaks (%)..
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