Abstract
Objectives
This study aims to identify the characteristics of domestic malaria by examining the status of malaria diagnoses referred to the Korea Disease Control and Prevention Agency (KDCA) between 2021 and 2025.
Methods
Malaria diagnostic samples referred to the KDCA were classified into private sector submissions from medical institutions and public sector submissions from public health centers and military hospitals. Malaria infection was confirmed by microscopic examination or molecular detection. Patient characteristics, such as parasitemia levels, were estimated using a formula based on real-time polymerase chain reaction (PCR) cycle threshold (Ct) values.
Results
The KDCA collected a total of 2,508 malaria-positive samples between 2021 and 2025. Domestic Plasmodium vivax accounted for 96.2% of malaria cases, whereas imported malaria cases were caused by Plasmodium falciparum (75.8%), Plasmodium ovale (16.8%), P. vivax (5.3%), and P. falciparum–P. ovale coinfection (2.1%). The proportion of diagnostic referrals from public health centers was peaked at 58.9% in 2023 and subsequently decreased, whereas the proportion from secondary hospitals gradually increased, reaching 43.8% in 2025. In contrast, the proportion from military hospitals markedly declined from 26.8% in 2024 to 9.9% in 2025. Based on parasitemia estimates calculated from real-time PCR Ct values, most patients in 2024–2025 showed parasitemia levels of 8,000/µl or higher.
Conclusions
Accurate malaria diagnosis is essential for effective disease prevention and control. This study is expected to facilitate patient management and contribute to national malaria elimination by providing basic information through an analysis of the status of malaria diagnosis over five years.
Keywords: Malaria, Microscopy, Molecular diagnosis
Key messages
① What is known previously?
In the Republic of Korea, Plasmodium vivax is endemic. All other malaria species are imported and account for approximately 3–4% of reported cases.
② What new information is presented?
The Korea Disease Control and Prevention Agency (KDCA) collected 90.4% of malaria samples between 2021 and 2025. Among diagnostic referrals, the proportion from public health centers decreased from 58.9% to 17.7%, and that from military hospitals decreased from 26.8% to 9.9%. However, the proportion from secondary hospitals increased from 8.7% to 43.8%. The average cycle threshold (Ct) value decreased from 25.8 to 25.6 in 2024–2025, whereas parasitemia increased from 72,870/µl to 80,433/µl.
③ What are implications?
KDCA produces basic data by analyzing the current status and characteristics of malaria diagnoses. Continuous surveillance is important for establishing public health policies that support malaria elimination.
Introduction
Malaria is an acute febrile illness transmitted by female Anopheles mosquitoes infected with Plasmodium parasites and has a significant impact on global public health [1]. The Plasmodium species known to infect humans include Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium knowlesi [2]. In the Republic of Korea (ROK), P. vivax malaria is endemic only in certain regions bordering North Korea, such as Gyeonggi, Incheon, and Gangwon provinces, and all other Plasmodium species occur only as imported cases [3]. Additionally, domestically acquired P. vivax malaria is characterized by the formation of hypnozoites in the liver, allowing a dormant period of up to 2 years [4].
A total of 559, 385, 294, 420, 747, 713, and 601 domestic malaria cases were reported in the ROK in 2019, 2020, 2021, 2022, 2023, 2024, and 2025, respectively, showing a decrease in malaria incidence during the coronavirus disease 2019 pandemic followed by repeated fluctuations. Confirmatory diagnosis of malaria includes microscopy, which directly identifies malaria parasites through blood smear examination, and molecular diagnostic tests, which detect malaria-related genes. As of 2025, microscopic examinations were conducted by the Korea Disease Control and Prevention Agency (KDCA), seven Institutes of Health and Environment (Seoul, Incheon, Gwangju, Gyeonggi, Northern Gyeonggi, Gangwon, and Chungnam), and 20 public health centers (Gapyeong-gun, Deogyang-gu, Ilsandong-gu, Ilsanseo-gu, Gimpo-si, Namyangju-si, Pocheon-si, Yangju-si, Yeoncheon-gun, Uijeongbu-si, Paju-si, Ganghwa-gun, Gyeyang-gu, Michuhol-gu, Bupyeong-gu, Seo-gu, Jung-gu, Goseong-gun, Cheorwon-gun, and Inje-gun). Moreover, molecular diagnostic testing was conducted by the KDCA, Regional Centers for Disease Control and Prevention, and 17 Institutes of Health and Environment (Seoul, Busan, Daegu, Incheon, Gwangju, Daejeon, Ulsan, Sejong, Gyeonggi Main and Northern Branch, Gangwon, Chungbuk, Chungnam, Jeonbuk, Jeonnam Main and Eastern Branch, Gyeongbuk, Gyeongnam, and Jeju) [5].
The Division of Vectors and Parasitic Diseases, KDCA, operates the National Reference Laboratory for Malaria to support effective national infectious disease management. It strengthens the diagnostic capacity of participating institutions through laboratory diagnostic training and proficiency testing, including private and public sector diagnostics, and enhances its own diagnostic capabilities and ensures the reliability of results through participation in external proficiency testing. Additionally, by biobanking and managing specimens from domestically acquired malaria cases, it serves as a control tower for diagnostic management.
This study aimed to identify the characteristics of domestic malaria incidence by summarizing the diagnostic status of private and public sector diagnostics referred to the Division of Vectors and Parasitic Diseases, KDCA, and specimens secured as resources during the recent five-year period (2021–2025), and thereby providing foundational data for a malaria elimination strategy.
Methods
1. Diagnostic Request
The Division of Vectors and Parasitic Diseases of the KDCA, in accordance with the “Notification on Testing and Examination of the KDCA,” accepts all test requests for specimens related to infectious diseases cases and manages diagnostic specimens by dividing them into private (healthcare institutions) and public (public health centers and military hospitals) sector.
2. Specimen Collection for Biobanking
Blood specimens submitted for diagnostic testing were transported via the KDCA Specimen Secure Transport System. For positive specimens not referred to the KDCA, residual specimens were collected and biobanked in cooperation with healthcare institutions and local public health centers.
3. Malaria Diagnosis
Malaria infection was confirmed for transported blood specimens by conducting microscopy or molecular diagnostic tests in accordance with the confirmatory test method requested by the referring institution and the standard operating procedures for infectious disease laboratory testing [6,7]. For microscopy, infection was confirmed by examining the thick smear slide, and species were identified by observing at least 100 microscopic fields on the thin smear slide. The molecular diagnostic test involved detecting a specific gene (18S ribosomal RNA) using nested polymerase chain reaction (PCR) and reading the results by electrophoresis. Diagnostic results were reported back through the Integrated Disease and Health Control System.
4. Results and Analysis of Characteristics of Positive Specimens
For the analysis, private and public sector requests and resource specimen acquisition cases handled by the Division of Vectors and Parasitic Diseases, KDCA, over the five-year period (2021–2025) were compiled to assess the diagnostic status and summarize the status by requesting institution. Beginning in 2024, to address the inefficiency of parasitemia calculation through microscopic examination, a formula was introduced to estimate parasitemia from real-time PCR cycle threshold (Ct) values using confirmed domestic P. vivax malaria specimens. As in conventional microscopy, a thick blood smears were examined to directly determine parasitemia based on parasites in asexual stages (ring forms, trophozoites, and schizonts), and the equation (y=−0.2785x+11.689, R²=0.8) was derived through regression analysis using parasitemia calculated as a Log value and the Ct value. Ct values ranges reported by Madamet et al. [8] were adopted. However, considering that the specimen distribution was concentrated at lower Ct values, the ranges were subdivided to define analytical categories based on data distribution.
Results
During 2021–2025, malaria molecular diagnostic tests referred to the Division of Vectors and Parasitic Diseases consisted of 928 private sector requests and 1,113 public sector requests (total: 2,041), accounting for 73.5% of the total number of reported patients during the same period. During this period, the highest number of diagnostic requests were recorded in 2023 (n=867) (Table 1). Among the 2,041 diagnoses, 816 malaria-positive (40.0%) and 1,225 malaria-negative cases (60.0%) were detected. A total of 2,508 malaria-positive specimens were biobanked, consisting of 816 positive cases confirmed by the Division of Vectors and Parasitic Diseases and 1,692 resource specimens confirmed at hospitals (Table 2). These specimens accounted for 90.4% of the 2,775 domestically acquired malaria cases during the same period.
Table 1. Status of diagnostic referral institutions (2021–2025).
| Category | 2021 | 2022 | 2023 | 2024 | 2025 | Total |
|---|---|---|---|---|---|---|
| Public health centers | 126 (50.2) | 184 (51.4) | 511 (58.9) | 66 (17.7) | 41 (21.4) | 928 |
| Military hospitals | 38 (15.1) | 65 (18.2) | 203 (23.4) | 100 (26.8) | 19 (9.9) | 425 |
| Primary clinics | 4 (1.6) | 1 (0.3) | 0 (0.0) | 12 (3.2) | 6 (3.1) | 23 |
| Secondary hospitals | 47 (18.7) | 31 (8.7) | 80 (9.2) | 130 (34.9) | 84 (43.8) | 372 |
| Tertiary hospitals | 25 (10.0) | 46 (12.8) | 44 (5.1) | 28 (7.5) | 24 (12.5) | 167 |
| Others | 11 (4.4) | 31 (8.7) | 29 (3.3) | 37 (9.9) | 18 (9.4) | 126 |
| Total | 251 (100.0) | 358 (100.0) | 867 (100.0) | 373 (100.0) | 192 (100.0) | 2,041 |
Unit: case (%).
Table 2. Malaria sample collection status (2021–2025).
| Category | 2021 | 2022 | 2023 | 2024 | 2025 | Total | |
|---|---|---|---|---|---|---|---|
| Medical institution | Positive/negative | 86/30 | 101/47 | 174/154 | 196/21 | 107/12 | 664/264 |
| Public institution | Positive/negative | 10/125 | 12/198 | 32/507 | 68/88 | 30/43 | 152/961 |
| Biobanking | Positive | 169 | 187 | 504 | 404 | 428 | 1,692 |
| Total | Positive/negative | 265/155 | 300/245 | 710/661 | 668/109 | 565/55 | 2,508/1,225 |
Of the 2,508 malaria-positive specimens secured from private and public sector through resource banking, 96.2% (2,413 cases) were domestically acquired P. vivax malaria, and the remaining 3.8% (95 cases) were identified as imported malaria. Imported malaria cases were predominantly P. falciparum malaria (75.8%, 72 cases), followed by P. ovale malaria (16.8%, 16 cases), imported P. vivax malaria (5.3%, 5 cases), and mixed P. falciparum/P. ovale malaria infections (2.1%, 2 cases) (Figure 1).
Figure 1. Malaria diagnosis in the Republic of Korea (2021–2025).
The status of institutions submitting private and public sector diagnostic requests showed that public health centers accounted for the highest proportion of requests (~50%) from 2021 to 2023; but thereafter, this proportion showed a declining trend, reaching approximately 19% (Table 1). In contrast, the rate of referrals to secondary hospitals showed a continuously increasing trend from 8.7% to 43.8%. For military hospitals, the referral rate gradually increased from 15.1% to 26.8% during 2021–2024, but decreased to 9.9% in 2025.
To analyze patterns of change in parasitemia, real-time PCR was performed on P. vivax malaria cases that occurred during January–December, 2024, and January–December, 2025. Parasitemia calculated from the measured Ct values was classified into six groups based on the parasitemia in the blood (Table 3). More than 95% of specimens investigated in 2024 and 2025 showed parasitemia values of 2,000/µl or greater. The mean Ct value for domestic P. vivax malaria patients decreased from 25.8 in 2024 to 25.6 in 2025, and correspondingly, the mean parasitemia increased from 72,870/µl to 80,433/µl.
Table 3. Classification of parasitemia according to Ct values of Plasmodium vivax malaria patients in the Republic of Korea (2024–2025).
| Category | Class Ⅰ | Class Ⅱ | Class Ⅲ | Class Ⅳ | Class Ⅴ | Class Ⅵ | Mean | |
|---|---|---|---|---|---|---|---|---|
| Real-time PCR Ct value |
32.9≤Ct<37 | 32.2≤Ct<32.9 | 30≤Ct<32.2 | 28≤Ct<30 | 25≤Ct≤28 | Ct<25 | 25.8 | |
| 25.6 | ||||||||
| Parasitemia (parasites/µl; P) |
P<300 | 300≤P<500 | 500≤P<2,000 | 2,000≤P<8,000 | 8,000≤P≤50,000 | 50,000<P | 72,870 | |
| 80,433 | ||||||||
| Sample number | 2024 | 3 | 3 | 23 | 60 | 273 | 247 | - |
| 2025 | 1 | 1 | 13 | 36 | 257 | 225 | - | |
| Interval (days; date of onset–date of diagnosis) |
2024 | 15.6±18.0 | 1.0±1.4 | 6.7±12.5 | 5.4±4.4 | 7.0±6.8 | 7.2±6.9 | 6.9±7.0 |
| 2025 | 0 | 0.3±0.5 | 5.4±5.3 | 5.1±7.6 | 5.1±7.9 | 3.9±4.4 | 4.5±6.2 | |
PCR=polymerase chain reaction; Ct=cycle threshold.
Conclusion
The Division of Vectors and Parasitic Diseases, KDCA, operates the National Reference Laboratory for Malaria with the aim of enhancing diagnostic capacity and ensuring reliability. It has also aided in effective specimen management by securing 90.4% of specimens from domestically acquired malaria cases over the past five years (2021–2025).
Because only P. vivax malaria is endemic in the ROK, all other malaria species can be classified as imported malaria. Imported malaria cases have been consistently reported each year, and epidemiological investigations have confirmed that most patients have a history of travel to Africa. Caution is warranted because the proportion of imported malaria cases has shown an increasing trend. Additionally, because different genotypes of P. vivax may be introduced through imported cases, continuous molecular epidemiologic surveillance in addition to diagnosis is important.
During 2021–2023, public health centers submitted the most diagnostic requests and showed a high rate of malaria-negative specimens. This finding might be attributed to their practice of requesting diagnostic testing as a proactive malaria control measure, such as post-treatment test-of-cure to confirm infection clearance in domestic malaria patients, or family testing conducted to enable early detection of recurrence and cluster cases. However, because repeated negative results were confirmed through the post-treatment test-of-cure and its contribution to additional patient management was assessed to be limited, the mandatory post-treatment test-of-cure requirement was lifted in 2024, and as the rate of family testing decreased, the number of referrals from public health centers also decreased. Currently, post-treatment test-of-cure is integrated into the patient follow-up management category and is operated in the form of a follow-up investigation conducted selectively as needed. The gradual increase in the number of diagnostic test requests from private healthcare institutions (primary and secondary hospitals) might be attributed to the enhancement of the capabilities of local public sector and laboratory personnel through various training programs in accordance with the Malaria Re-elimination Action Plan, leading to active recommendations for testing by local public health centers. The high number of diagnostic requests at military hospitals in 2023 might be attributed to the screening conducted on soldiers returning from deployment. Testing was conducted as a preemptive measure even in individuals without malaria symptoms, and most tested negative. The referrals from military hospitals decreased to 9.9% in 2025 because the requests for testing were consolidated to the Armed Forces Medical Research Institute in order to reduce the burden on military hospitals of having to submit specimens twice, to both the Armed Forces Medical Research Institute and the KDCA. To ensure continuity of epidemiologic analysis for discharged soldiers diagnosed at private healthcare institutions, the two institutions are strengthening cooperation regarding the sharing of diagnostic results and malaria genetic information.
Parasitemia is a key indicator of the level of malaria infection, providing important information for assessing disease severity, monitoring treatment response, and predicting prognosis. Additionally, changes in parasitemia are also useful for evaluating the associations with diagnostic test results. Calculating a malaria patient’s parasitemia requires microscopic examination of a thick smear slide, which is time-consuming. In addition, the examiner’s proficiency can greatly affect the results. As real-time PCR has become more common, a study has been conducted in the ROK to derive a correlation equation between parasitemia confirmed by microscopic examination and real-time PCR Ct values in malaria patients [9]. The Division of Vectors and Parasitic Diseases also used specimens from 2024 and 2025 to derive a correlation equation (y=−0.2785x+11.689, R²=0.8) through regression analysis using parasitemia calculated as a Log value and real-time PCR Ct values. This approach has made it possible to estimate parasitemia from the Ct values of positive specimens, and it will be used for future malaria epidemic analysis. Most P. vivax malaria patients in the ROK in 2024–2025 were confirmed to have Ct values of <25 or 25–28 (Table 3). However, cases of low-level infection with a Ct value of ≥32.2 (parasitemia≤2,000/µl) were also often identified. A 2011 study that confirmed parasitemia in domestic malaria patients (mean, 8,396/μl) also reported a low-level infection case with a parasitemia of 12/μl [10]. Cases of low-level infection may be difficult to detect during the diagnostic process due to relatively low parasite density. Therefore, it is necessary to monitor the distribution of parasitemia and changes in diagnostic patterns through continuous surveillance and to supplement diagnostic strategies accordingly. Regarding the relationship between parasitemia and time to diagnosis, in 2025, the time to diagnosis showed a decreasing trend as parasitemia increased, whereas in 2024, no consistent pattern in time to diagnosis was observed. This discrepancy might be influenced by various factors, such as the severity of clinical symptoms and the timing of testing. Additionally, the average time to diagnosis decreased in 2025, when parasitemia increased, but these results are difficult to generalize because of the large Class V and VI populations (Table 3). Additionally, because the time to diagnosis can be influenced by various factors beyond the testing process, such as the timing of a patient’s visit to a healthcare institution and the specimen submission process, these results should be interpreted as exploratory analysis. Therefore, further analysis of specimens from various classes is necessary to determine the correlation.
This study analyzed the status of malaria diagnosis in the ROK from 2021 to 2025. The causes of changes in malaria incidence were estimated by analyzing the diagnostic request patterns by institutions based on malaria specimens collected and preserved over the five-year period. Additionally, the characteristics of domestic malaria were identified by estimating patient parasitemia. These results may provide evidence to support the development of malaria elimination policies, including strengthening the domestic malaria surveillance system, establishing strategies for early diagnosis and prompt treatment, and improving diagnostic accessibility across healthcare institutions.
Acknowledgments
None.
Declarations
Ethics Statement: Not applicable.
Funding Source: Korea Disease Control and Prevention Agency (6331-301-210-13).
Conflict of Interest: The authors have no conflicts of interest to declare.
Author Contributions: Conceptualization: HIL. Data curation: HNJ. Formal analysis: HNJ. Funding acquisition: HIL. Investigation: HNJ, BRK. Project administration: HIL. Visualization: HNJ. Writing – original draft: HNJ. Writing – review & editing: IHK, HIL.
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