Vegetable intake, but not fruit intake, is associated with a reduction in the risk of cancer incidence and mortality in middle-aged Korean men.

BACKGROUND: Few prospective studies have examined the preventive role of fruit and vegetable intakes against cancer in Asian populations. OBJECTIVE: This prospective study evaluated the associations between total fruit intake, total vegetable intake, and total fruit and vegetable intake and total cancer incidence and mortality. METHODS: This prospective cohort study included 14,198 men 40-59 y of age enrolled in the Seoul Male Cohort Study from 1991 to 1993. Fruit and vegetable intakes were assessed by a validated food-frequency questionnaire. We used Cox proportional hazard regression models to compute RR ratios and 95% CIs. RESULTS: During the follow-up period from 1993 to 2008, 1343 men were diagnosed with cancer, and 507 died of cancer. Total vegetable intake was linearly associated with cancer incidence but was nonlinearly associated with cancer mortality; by comparing ≥ 500 g/d with <100 g/d of total vegetable intake, the multivariable-adjusted RR for total cancer incidence was 0.72 (95% CI: 0.58, 0.90; P-trend: 0.02; P-nonlinearity: 0.06). For total cancer mortality, the multivariable-adjusted RRs comparing 100 to <200 g/d, 200 to <300 g/d, 300 to <500 g/d, and ≥ 500 g/d with <100 g/d of total vegetable intake were 0.68 (95% CI: 0.53, 0.88), 0.75 (95% CI: 0.57, 0.98), 0.72 (95% CI: 0.54, 0.95), and 0.67 (95% CI: 0.47, 0.95), respectively (P-trend: 0.09; P-nonlinearity: 0.01). No associations were found between total fruit intake and total cancer incidence and mortality; ≥ 300 g/d vs. <50 g/d, RR: 1.04 (95% CI: 0.87, 1.25; P-trend = 0.56) for incidence and RR: 0.89 (95% CI: 0.66, 1.21; P-trend = 0.71) for mortality. CONCLUSIONS: Our findings suggest that total vegetable intake is linearly associated with cancer incidence but nonlinearly associated with total cancer mortality in middle-aged Korean men. However, total fruit intake is not associated with total cancer incidence or mortality.

Statin Use and Liver Cancer Risk: A Meta-Epidemiological Study of Retrospective Cohort Studies by the Types of Constructed Cohort.

OBJECTIVE: Previous systematic reviews of retrospective cohorts (RSC) indicate that statin use decreases the risk of liver cancer. However, the summary effect size (sES) of the randomized controlled trials was not statistically significant. This study aimed to conduct a subgroup meta-analysis based on the types of constructed cohorts. METHODS: RSCs were selected from previous systematic reviews. Based on the characteristics of the source database (national vs. hospital) and the selection criteria of the subjects (population vs. patients), RSCs were categorized into three types of study cohorts: a national-based population cohort (NPo), national-based patient cohort (NPa), and hospital-based patient cohort (HPa). The sES and 95% confidence intervals were calculated using a random-effects model. RESULT: The 28 cohorts from 23 RSC were classified into 15 NPa, 7 NPo, and 6 HPa. The sES of 15 NPa decreased the liver cancer risk with statin intake history with statistical significance, but 7 NPo lost statistical significance. CONCLUSION: The lack of statistical significance in NPo supports the argument that the conclusions of existing systematic reviews on RSC have low validity. It is necessary to conduct a subgroup meta-analysis of the NPo, NPa, and HPa proposed in this study when conducting a systematic review of RSCs, which will evaluate various outcomes of a specific drug intake with time-varying exposure.

Survey of controversial issues of end-of-life treatment decisions in Korea: similarities and discrepancies between healthcare professionals and the general public.

INTRODUCTION: End-of-life (EOL) treatment issues have recently gained societal attention after the Korean Supreme Court's ruling that the presumed wishes of an elderly woman in a persistent vegetative state (PVS) should be honored. We tried to evaluate what Koreans thought about controversial issues regarding EOL treatments. METHODS: We surveyed Koreans with the following questions: 1) are ventilator-dependent PVS patients candidates for end-of life treatment decisions? 2) Is withholding and withdrawing EOL treatment the same thing? 3) In an unconscious, terminally ill patient, whose wishes are unknown, how should EOL decisions be made? 4) How should we settle disagreement amongst medical staff and the patient's family on EOL decisions? RESULTS: One thousand Koreans not working in healthcare and five hundred healthcare professionals responded to the survey. Fifty-seven percent of Koreans not working in healthcare and sixty seven percent of Korean healthcare professionals agreed that ventilator-dependent PVS patients are candidates for EOL treatment decisions. One quarter of all respondents regarded withholding and withdrawing EOL treatment as equal. Over 50% thought that EOL treatment decisions should be made through discussions between the physician and the patient's family. For conflict resolution, 75% of Koreans not working in healthcare preferred direct settlement between the medical staff and the patient's family while 55% of healthcare professionals preferred the hospital ethics committee. CONCLUSIONS: Unsettled issues in Korea regarding EOL treatment decision include whether to include ventilator-dependent PVS patients as candidates of EOL treatment decision and how to sort out disagreements regarding EOL treatment decisions. Koreans viewed withholding and withdrawing EOL treatment issues differently.

Lung cancer incidence by smoking status in Korean men: 16-years of observations in the Seoul Male Cancer Cohort study.

The relative risk (RR) of smoking and mortality of lung cancer in British doctors was previously reported to have increased throughout a 40-yr period. Here, we evaluated this RR based on the incidence of lung cancer in Korean men using a longer follow-up period. We compared our data to the RR reported in a study using a 10-yr follow-up period; the subjects and methods were identical to those of the previous paper with the exception of the follow-up period, which ended on December 31, 2008. We found that the RR of smoking habits in patients with lung cancer did not increase, and that the data showed narrowing 95% confidence intervals over a longer observation in Korean men. Estimated lung cancers attributable to smoking were 55.6%. These results highlight the need for an intervention program to help patients quit smoking in Korea.

Pulmonary tuberculosis and lung cancer risk in current smokers: the Seoul Male Cancer Cohort Study.

Authors evaluated pulmonary tuberculosis (PTB) history as a risk factor for lung cancer in current male smokers in a prospective, population-based cohort study. The subjects were the 7,009 males among the participants in the Seoul Male Cancer Cohort Study for whom there was full information on PTB history and smoking habits. With a 16-yr follow-up, 93 cases of lung cancer occurred over the 99,965 person-years of the study. The estimated relative risk (RR) of PTB history of current smokers in lung cancer after adjusting for three confounders - intake of coffee and tomatoes, and age at entry - was 1.85 (95% CI: 1.08-3.19). The observed joint RRs and attributable risks (ARs) across strata of three confounders were greater than the expected, indicating a positive interaction. Thus a history of PTB in current smokers may be another risk factor for lung cancer. Based on a synergic interaction, a heavy male smoker with a PTB history would be expected to belong to the group at high risk of lung cancer.

Combined primary tumor and extracranial metastasis status as constituent factor of prognostic indices for predicting the overall survival in patients with brain metastases.

We retrospectively analyzed the prognostic factors on overall survival (OS) in patients with brain metastasis (BM) and evaluated the role of combined primary tumor and extracranial metastasis (ECM) status as a constituent factor for prognostic index. This study involved 897 patients with BMs who underwent radiotherapy between April 2003 and December 2009. Among the clinical parameters, multivariate analysis showed that age, Karnofsky performance status (KPS), combined primary tumor and ECM status, number of BMs, and treatment group were significant prognostic factors for OS (P < 0.05). To compare the discriminatory ability of 5 prognostic indices, i.e., recursive partitioning analysis (RPA), basic score for BMs (BSBM), score index for radiosurgery (SIR), graded prognostic assessment (GPA), and modified GPA including the combined primary tumor and ECM status (mGPA), the Akaike information criteria (AIC) were calculated. The mGPA showed the lowest AIC value, followed by RPA, GPA, SIR, and BSBM, in that order. It is implicated that modified score of pre-existing factors (i.e., age and KPS) and addition of the combined primary tumor and ECM status to the prognostic index can improve its discriminatory ability and the combined primary tumor and ECM status may be useful as one of constituent factors for prognostic index.

Trends of legionellosis reported in Jeju Province, Republic of Korea, 2015-2022.

BACKGROUND: The number of reported cases of Legionnaires' disease (LD) in the Republic of Korea surged nationally in 2016; however, in 2022, this number was higher in Jeju Province than the previous national peak. A descriptive epidemiological study was conducted to analyze trends in the incidence of reported LD cases in Jeju Island from 2015 to 2022. METHODS: The data for this study were obtained from case reports submitted to the Korea Disease Control and Prevention Agency through its Disease and Health Integrated Management System. The selection criteria were cases or suspected cases of LD reported among Jeju residents between 2015 and 2022. The 95% confidence interval of the crude incidence rate was calculated using the Poisson distribution. RESULTS: Since 2020, the incidence rate of LD in Jeju has risen sharply, showing a statistically significant difference from the national incidence rate. A particular medical institution in Jeju reported a significant number of LD cases. Screening with the urine antigen test (UAT) also increased significantly. CONCLUSION: Our findings indicate that the rapid increase in cases of LD in Jeju Province since 2020 was due to the characteristics of medical-care use among Jeju residents, which were focused on a specific medical institution. According to their clinical practice guidelines, this medical institution conducted UATs to screen patients suspected of pneumonia.

Epidemiological investigation of a food-borne outbreak in a kindergarten, Jeju Province, Korea.

OBJECTIVES: On Monday, September 6, 2021, at a kindergarten in Jeju Province, a large number of children vomited and developed food poisoning symptoms, and this necessitated an epidemiological investigation. METHODS: The team surveyed symptoms and food intake history of kindergarten children, teachers, and workers who ate lunch between September 2 (Thursday) and September 6 (Monday), excluding weekends. In addition to rectal swabs, environmental samples from preserved foods, cooking utensils, drinking water, and refrigerator handles were collected. Pulsed field gel electrophoresis (PFGE) for genetic fingerprint analysis was also performed. RESULTS: There were 19 cases among 176 subjects, which indicated an attack rate of 10.8%. The epidemic curve showed a unimodal shape, and the average incubation period was 2.6 hours. While no food was statistically significant in food intake history, the analysis of 35 rectal smear samples detected Bacillus cereus in 7 children, 4 teachers, and 1 cooking staff. Enterotoxins were also detected in 12 samples. Out of 38 environmental samples, B. cereus and enterotoxins were detected in the morning snack cereal, lunch bean sprouts, and afternoon snack steamed potatoes on Monday, September 6th. The result of the PFGE test on 10 isolates of B. cereus showed that there was no genetic homology. CONCLUSIONS: Our results indicated that this outbreak was simultaneously caused by various strains of B. cereus from the environment.

Low cholesterol is associated with mortality from cardiovascular diseases: a dynamic cohort study in Korean adults.

This study was conducted to evaluate the association of single serum total cholesterol (TC) measurement with cardiovascular diseases (CVD) deaths in Korean adults. The study subjects were taken from the multi-site collaborative dynamic prospective cohort for epidemiologic investigation on cancer risk in residents nearby nuclear power plants in Korea. A total of 12,740 adults aged 40 to 69 yr who underwent a mass screening examination were followed up from 1993 to 2008. Occurring CVD deaths were confirmed by the death certificates in the National Statistical Office, Korea. Groups with the lowest group having TC < 160 mg/dL as well as the highest group having >= 240 mg/dL were associated with higher CVD mortality in Cox proportional hazards analysis adjusting for age, sex, smoking and drinking status, body mass index, level of blood pressure, triglyceride and high density lipoprotein cholesterol. The distribution of adjusted hazard ratios showed the U-shaped curve. Based on the results of this study, caution should be taken in prescribing statins for primary prevention among people at low cardiovascular risk in Korean adults.

Diabetes History and Gastric Cancer Risk: Different Results by Types of Follow-Up Studies.

OBJECTIVE: The previous systematic reviews evaluating the association between diabetes history and gastric cancer risk showed inconsistent results. The aim was to check through a meta-epidemiological study that the conclusions of systematic reviews evaluating the association between diabetes history and gastric cancer risk might differ by the type of follow-up study. METHODS: The potential study subjects were follow-up studies selected from the seven systematic reviews obtained by searching PubMed using diabetes and gastric cancer keywords. The selection criterion was defined as a follow-up study for evaluating the association between the history of type 2 diabetes mellitus and the incidence of gastric cancer. And the values of RR and its 95%CI, which adjusted for the most confounders in each paper, were extracted for meta-analysis. A random-effects model meta-analysis by types of the follow-up study and sex group was performed. RESULTS: A total of 25 follow-up studies were finally selected for meta-analysis. They were classified into 16 retrospective and 9 prospective studies in types of follow-up study. The statistical significance between diabetes history and gastric cancer risk was found in retrospective studies (sRR=1.17, 95%CI: 1.02-1.34, I-squared =91.0%) but disappeared in prospective studies (sRR=1.09, 95%CI: 0.91-1.29, I-squared = 68.6%). Even in the analysis of subgroups by sex, statistical significance was not found in the prospective study, consistently. CONCLUSION: The main reason for the previous meta-analysis's diverse results for the association between diabetes history and gastric cancer risk was that the type of follow-up study was not reflected. According to the meta-analysis of prospective cohort studies, it could be concluded that there is no association between diabetes history and gastric cancer risk.

Circulating 25-hydroxyvitamin D levels and hypertension risk after adjusting for publication bias.

BACKGROUND: Previous systematic reviews reported that serum vitamin D deficiency was associated with risk of hypertension. The aim was to conduct a meta-epidemiological analysis for evaluating the potential effects of publication bias. METHODS: The selection criterion was defined as a follow-up study for evaluating the association between circulating 25-hydroxyvitam D level and hypertension risk in adults. A funnel plot and Egger's test were used to detect a publication bias. If a publication bias was identified, trim-and-fill analysis (TFA) with linear estimator was performed to estimate a summary relative risk (sRR). RESULTS: The meta-analysis of 13 cohorts resulted in the lower the vitamin D, the higher the risk of hypertension statistically significant (sRR, 1.22; 95% confidence interval [CI], 1.05 to 1.41). But The P-value of Egger's test (=0.015) and asymmetry of the funnel plot showed that there was a publication bias. TFA resulted in that statistical significance disappeared in the association between vitamin D level and hypertension risk in total cohorts (filled sRR, 1.03; 95% CI, 0.89 to 1.18) as well as men and women cohorts. CONCLUSIONS: The publication bias-adjusted results by TFA had no statistically significant association between vitamin D levels and the risk of hypertension. The significant results in previous systematic reviews might be interpreted as due to publication bias.

Statin Intake and Gastric Cancer Risk: An Updated Subgroup Meta-analysis Considering Immortal Time Bias.

A retrospective record-linkage study (RLS) based on medical records containing drug prescription histories involves immortal time bias (ITB). Thus, it is necessary to control for this bias in the research planning and analysis stages. Furthermore, a summary of a metaanalysis including RLSs that did not control for ITB showed that specific drugs had a preventive effect on the occurrence of the disease. Previous meta-analytic results of three systematic reviews evaluating the association between statin intake and gastric cancer risk showed that the summary hazard ratio (sHR) of the RLSs was lower than 1 and was statistically significant. We should consider the possibility of ITB in the sHR of RLSs and interpret the results carefully.

Diagnostic value of peritumoral minimum apparent diffusion coefficient for differentiation of glioblastoma multiforme from solitary metastatic lesions.

OBJECTIVE: In glioblastoma multiforme, the peritumoral region may be infiltrated with malignant cells in addition to vasogenic edema, whereas in a metastatic deposit, the peritumoral areas comprise predominantly vasogenic edema. The purpose of this study was to determine whether the minimum apparent diffusion coefficient (ADC) can be used to differentiate glioblastoma from solitary metastasis on the basis of cellularity levels in the enhancing tumor and in the peritumoral region. MATERIALS AND METHODS: Seventy-three patients underwent conventional MRI and diffusion-weighted imaging (DWI) before undergoing treatment. The minimum ADC was measured in the enhancing tumor, peritumoral region, and contralateral normal white matter. To determine whether there was a statistical difference between metastasis and glioblastoma, we analyzed patient age and sex, minimum ADC value, and ADC ratio of the two groups. A receiver operating characteristic (ROC) curve analysis was used to determine the cutoff value of the minimum ADC that had the best combination of sensitivity and specificity for distinguishing between glioblastoma and metastasis. RESULTS: The mean minimum ADC values and mean ADC ratios in the peritumoral regions of glioblastomas were significantly higher than those in metastases. However, the mean minimum ADC values and mean ADC ratios in enhancing tumors showed no statistically significant difference between the two groups. According to ROC curve analysis, a cutoff value of 1.302 × 10(-3) mm(2)/s for the minimum peritumoral ADC value generated the best combination of sensitivity (82.9%) and specificity (78.9%) for distinguishing between glioblastoma and metastasis. CONCLUSION: Although the characteristics of solitary metastasis and glioblastoma multiforme may be similar on conventional MRI, DWI can offer diagnostic information to distinguish between the tumors.

Thyroid cysts treated with ethanol ablation can mimic malignancy during sonographic follow-up.

PURPOSE: We aimed to assess long-term ultrasound (US) findings after US-guided percutaneous ethanol ablation (EA) in benign thyroid cysts and predominantly cystic thyroid nodules. METHODS: Forty patients with thyroid cysts (n = 14) and predominantly cystic thyroid nodules (n = 26) underwent long-term US follow-up (range, 12-36 months; mean, 18.2 months) after EA. US images of 40 post-EA nodules were retrospectively investigated to study the reduction in nodule volume and detailed US appearance. RESULTS: On follow-up US, post-EA nodules showed the following features: Marked hypoechogenicity (n = 28), spiculated margin (n = 7), microcalcifications (n = 6), taller-than-wide shape (n = 2), centrally predominant vascularity (n = 3), no vascularity (n = 31), mixed vascularity (n = 3), and peripheral vascularity (n = 3). Post-EA nodules were diagnosed by US as benign (n = 3), probably benign (n = 2), borderline (n = 5), possibly malignant (n = 20), and malignant (n = 10). No statistical difference in the incidence of malignant US findings was observed between thyroid cysts and predominantly cystic thyroid nodules (p > 0.05, Fisher's exact test). CONCLUSIONS: Long-term follow-up US after successful EA of benign thyroid cysts and predominantly cystic thyroid nodules revealed a high incidence of findings that are usually associated with malignancy. Recognizing these consequences of the procedure would help avoid unnecessary FNA on post-EA nodules.

Human papillomavirus infection and gastric cancer risk: A meta-epidemiological review.

Gastric cancer (GC) is a multifactorial disease, and several modifiable risk factors have been reported. This review summarizes and interprets two previous quantitative systematic reviews evaluating the association between human papillomavirus (HPV) infection and GC risk. The results of two systematic reviews evaluating the same hypothesis showed a statistically significant difference in summary odds ratios and their 95% confidence intervals. Thus, it is necessary to conduct a subgroup analysis of Chinese and non-Chinese studies. Additional meta-analyses that control for heterogeneity are required. Reanalysis showed that all the Chinese studies had statistical significance, whereas the non-national studies did not. The funnel plot asymmetry and Egger's test confirmed publication bias in the Chinese studies. In addition, the proportion of HPV-positive cases in Chinese studies was 1.43 times higher than that in non-Chinese studies and 2.81 times lower in controls. Therefore, the deduced evidence is currently insufficient to conclude that HPV infection is associated with GC risk.

Coffee consumption and risk of type 2 diabetes mellitus in Asians: A meta-epidemiological study of population-based cohort studies.

BACKGROUND: Previous systematic reviews have consistently reported that coffee consumption has a preventive effect on the occurrence of type 2 diabetes mellitus (T2DM). However, further evaluations between coffee consumption and the risk of T2DM in Asian populations are needed. AIM: To conduct a meta-epidemiological study on systematic reviews evaluating the association between coffee consumption and the risk of T2DM in Asian people. METHODS: The selection criterion was defined as a population-based prospective cohort study evaluating the association between coffee consumption and the risk of T2DM in Asian populations, reporting the adjusted relative risk (RR) and its 95% confidence interval (CI) for potential confounders. A fixed-effect model meta-analysis was applied to calculate the summary RR and its 95%CI in less than 50% of the I 2 value indicating the level of heterogeneity. A two-stage fixed-effects dose-response meta-analysis (DRMA) was performed to calculate the risk per unit dose (a cup per day). RESULTS: A total of seven studies were selected in this meta-epidemiological study. The risk of T2DM in Asian populations was significantly reduced in the highest to the lowest dose group (summary RR = 0.73, 95%CI: 0.66-0.82; I 2 value = 0.0%). The DRMA showed that drinking one cup of coffee per day reduced the risk of T2DM in Asian populations by 8% (RR = 0.92, 95%CI: 0.90-0.95). CONCLUSION: These findings support the conclusion that coffee consumption has a protective effect on the occurrence of T2DM in Asian men and women.

Use of oral contraceptives and risk of pancreatic cancer in women: A recalculated meta-analysis of prospective cohort studies.

In a recent systematic review and meta-analysis of observational studies, the author found potential errors in the selection and extraction processes. The recalculated summary relative risks and the results of a dose-response meta-analysis showed that oral contraceptive use may not be associated with the risk of pancreatic cancer in women.

Hormonal Replacement Therapy and Risk of Thyroid Cancer in Women: A Meta-Epidemiological Analysis of Prospective Cohort Studies.

OBJECTIVES: Many experimental studies have reported that female sex hormones involve thyroid cancer development because the incidence rate of thyroid cancer in women (TCW) is 3 times higher than in men. Three previous systematic reviews reporting no association between hormone replacement therapy (HRT) and TCW risk had the same search year of 2014. The aim was to reevaluate the association between HRT use and TCW risk using a meta-epidemiological study of prospective cohort studies. METHODS: The study preferentially used all studies selected by the existing systematic reviews and then secured an additional cohort from the list citing the studies. The selection criterion was defined as the prospective cohort study assessing the association between HRT and TCW risk by adjusted relative risk and its 95% confidence intervals (CI) from multivariate analysis. A random-effects model meta-analysis was applied to estimate summary relative risk (sRR) and its 95% CI. A publication bias was evaluated by Egger's test; moreover, the statistical significance level was set at 5%. RESULTS: Nine cohort studies were finally selected. The random-effect model was applied because of heterogeneity (I² = 64.3%). The sRR and its 95% CI from a random-effects model meta-analysis had no statistical significance in the association between HRT and TCW risk (sRR = 1.11; 95% CI, 0.98-1.26). Additionally, Egger's test revealed no statistical significance (P = 0.91). CONCLUSIONS: HRT is not associated with TCW risk based on the random-effects model meta-analysis of prospective cohort studies published until now.

Sex as an effect modifier in the association between alcohol intake and gastric cancer risk.

BACKGROUND: The results of previous meta-analyses evaluating the association between the alcohol intake and gastric cancer risk have reported that a statistical significance only for men. AIM: To investigate the different association between alcohol intake and gastric cancer risk between men and women. METHODS: The selection criteria included a prospective cohort study for evaluating alcohol intake and gastric cancer risk, with relative risks adjusted for potential confounders. Adjusted relative risk (RR) for the potential confounders and its 95% confidence interval (CI) in the highest vs lowest level were extracted from each study and a random-effects meta-analysis was conducted. Subgroup analyses by region, level of adjustment for smoking status, adjusting for body mass index, and year of publication were conducted. RESULTS: A meta-analysis of all 27 cohorts showed that alcohol intake increased the risk of gastric cancer (summary RR = 1.13, 95%CI: 1.04-1.23, I 2 = 58.2%). Further, 13 men's cohorts had higher summary RR while maintaining statistical significance, and only seven women's cohorts had no statistical significance. CONCLUSION: The present review suggests that alcohol consumption increases the risk of gastric cancer in men. These findings showed that the sex variable in the association between alcohol intake and gastric cancer risk seemed to be an effect modifier with an interaction term. It is necessary to re-estimate follow-up outcomes after stratifying for sex.

Sources of Infection Among Confirmed Cases of COVID-19 in Jeju Province, Korea.

OBJECTIVES: Jeju Province in Korea reported 627 coronavirus disease 2019 (COVID-19) cases between January 20, 2020, and March 31, 2021. This study analyzed the sources of infection among confirmed cases in Jeju Province, a self-governed island. METHODS: The sources of infection were broadly categorized as follows: (1) infections from overseas (confirmed patients who reported travel overseas or contact with overseas travelers); (2) infections from outside Jeju Province (confirmed patients who had visited other provinces or had contact with individuals who had traveled to other provinces in Korea); and (3) unknown sources of infection (confirmed patients who were infected following contact with an infected person whose source of infection was unknown). The chi-square test was used to analyze the differences in the distributions of related variables for each source of infection. RESULTS: Of the 627 confirmed cases, 38 (6.1%) were infections from overseas sources, 199 (31.7%) were from outside of Jeju Province, and 390 (62.2%) were from unknown sources. Jeju Province had no cases with an unknown source of infection during the first and second waves of the nationwide outbreak. CONCLUSIONS: Infections from overseas sources could be blocked from spreading to local communities in Jeju Province by conducting screening at the airport, along with the preemptive suspension of visa-free entry. In addition, considering the scale of the nationwide outbreak, measures must be established to delay outbreaks from unknown sources of infection caused by sources outside Jeju Province.