Introduction
Dengue is a vector-borne viral disease transmitted mainly by
Aedes aegypti and
Aedes albopictus mosquitoes [
1]. Driven by climate change and globalization, nearly half of the world’s population is now at risk of infection. Increased international travel has significantly contributed to the global spread of the dengue virus [
2]. In 2014, a major outbreak occurred in Japan after a traveler returning from a dengue-endemic country introduced the virus, leading to local transmission and 160 infections [
3]. In the Republic of Korea, 100 to 200 imported dengue cases are reported each year, highlighting the importance of rigorous entry-point surveillance [
4]. To prevent domestic introduction, the Korea Disease Control and Prevention Agency (KDCA) has implemented a series of countermeasures. On December 1, 2023, dengue was formally designated a quarantinable infectious disease, further strengthening surveillance and early detection systems [
5]. While several studies have examined dengue surveillance at entry points, no research has investigated patient characteristics and response processes spanning from the initial detection of suspected cases to final confirmation [
6–
8]. This study therefore analyzes the characteristics and response procedures of dengue rapid diagnostic testing (RDT) cases detected at Gimhae International Airport between 2022 and 2024. The airport manages approximately 10,000 flights and 15 million passengers annually, making it a critical site for monitoring imported infections. The findings aim to provide practical insights for enhancing quarantine operations in the future.
Materials and Methods
Study Design
From July 1, 2022, to December 31, 2024, a total of 334 travelers who entered the Republic of Korea through Gimhae International Airport after visiting dengue-designated quarantine regions and underwent RDT were included in this study. The study population comprised individuals subject to mandatory testing under public health regulations as well as those who voluntarily requested testing. All participants provided informed consent for dengue RDT. Mandatory testing was applied to travelers with a history of mosquito bites during their trip who presented with dengue-related symptoms—such as fever, headache, or rash—at the time of entry. These individuals were classified as suspected dengue cases. In contrast, voluntary testers were those who, either at the time of entry or within 7 days thereafter, experienced mosquito bites or dengue-like symptoms and requested testing on their own initiative.
RDT for Dengue
Two commercial kits were used: Asan Easy Test Dengue NS1 Ag and Asan Easy Test Dengue immunoglobulin (Ig) G/IgM (Asan Pharm Co., Ltd.). These kits detect the DENV NS1 antigen (sensitivity, 97.16%; specificity, >99.9%) and IgG/IgM antibodies (IgG sensitivity, 98.29%; IgG specificity, 97.76%; IgM sensitivity, 97.92%; IgM specificity, 100%) in serum samples. For the procedure, whole blood was collected from the fingertip using a lancet. Approximately 100 µL (3 drops) of blood was then applied to the test kit directly or with a disposable dropper. After 15 to 20 minutes, the results were interpreted. A test was considered negative if a color band appeared only on the control line (C), and positive if color bands appeared on both the control line (C) and the test line (T). All procedures followed the manufacturer’s instructions.
Traveler Dengue Virus Testing Procedure
At the quarantine station, travelers with positive RDT results were directed to a public health center or hospital for further evaluation. At these medical institutions, blood samples were collected and forwarded to the Institute of Public Health and Environment, the designated confirmatory diagnostic institution (
Figure 1).
Dengue Virus Laboratory Diagnosis
To confirm dengue virus infection, whole blood specimens from the 12 RDT-positive individuals were analyzed at the Institute of Public Health and Environment. Confirmatory testing included real-time reverse transcription polymerase chain reaction (RT-PCR) for NS1 antigen detection and IgM/IgG enzyme-linked immunosorbent assays (ELISAs) targeting envelope- and membrane-specific antibodies [
9,
10]. A case was considered confirmed if dengue virus-specific genetic material was detected by PCR, or if a fourfold or greater increase in antibody titers was observed in convalescent-phase serum compared with the acute-phase sample.
IRB Approval
This study protocol was approved by the Institutional Review Board of the KDCA. The Ethics Committee waived the requirement for individual informed consent (approval number: KDCA-2025-08-01-PE-01).
Results
Among the 334 travelers who underwent RDT for dengue, 12 tested positive, and 3 were confirmed positive through diagnostic testing. By sex, males accounted for 176 cases (52.7%), slightly outnumbering females (158 cases, 47.3%). The largest age group was individuals in their 20s and 30s, with 194 cases (58.1%). Vietnam was the most common country of departure, reported in 138 cases (41.3%). The most frequent travel duration was 5 days or less, observed in 162 cases (48.5%). A large majority of RDTs were conducted on Korean nationals (98.2%). No confirmed dengue cases were identified among foreign nationals, asymptomatic travelers, or those who traveled for 10 days or less.
To evaluate the relationship between RDT band intensity and confirmatory diagnostic outcomes, we analyzed the 12 RDT-positive cases. Excluding one case in which confirmatory testing was not performed, the remaining 11 were classified into 5 levels according to RDT intensity. All 7 cases with marginally positive RDT results were confirmed negative (0%) through diagnostic testing. In contrast, among the 4 cases with RDT intensity categorized as weakly positive or higher, 3 (75.0%) were confirmed positive.
Symptomatic travelers with positive RDT results were referred to medical institutions for confirmatory diagnostic testing in accordance with the “Traveler Dengue Virus Testing Procedure,” where blood samples were collected (
Figure 1). To evaluate the timeliness of confirmatory reporting, we compared the interval between sample collection and result notification by institution type and day of the week. Hospitals required an average of 4.00 days to report results, whereas public health centers required 2.71 days. Samples collected on weekdays had a shorter mean turnaround time (2.33 days) than those spanning weekends (5.00 days). Notably, hospital-based samples collected over weekends took an average of 5.33 days, while all 5 samples collected at public health centers on weekdays were reported by the following day.
All 3 dengue cases detected early at the point of entry involved travelers to Vietnam, Indonesia, or both, with more than 10 days elapsed between departure and RDT screening. Common symptoms included fever, chills, headache, and itching. Two patients reported mosquito bites, while one was uncertain (
Table 1). In every confirmed case, the RDT showed an intensity of weakly positive or higher (
Figure 2).
Discussion
In this study, we analyzed 334 cases of dengue RDT performed at the quarantine stage to detect imported cases early, including 12 RDT-positive cases. All confirmed dengue cases presented with typical symptoms such as fever and headache. Although some travelers requested testing following mosquito bites, the participation of asymptomatic individuals remained low due to the symptom-based screening approach, and no asymptomatic infections were identified (
Table 2).
Three dengue cases were confirmed at the point of entry, and all had a travel history involving Indonesia and Vietnam. These 2 countries, along with the Philippines and Thailand, have consistently accounted for a large proportion of imported dengue cases in the Republic of Korea in recent years, underscoring the need for proactive testing among travelers returning from these regions [
11]. All 3 confirmed patients reported dengue-related symptoms such as fever and headache. While testing was also available to individuals who reported mosquito bites, the symptom-based screening strategy resulted in limited participation from asymptomatic travelers, and no asymptomatic cases were detected (
Table 2). Given that asymptomatic infections may account for up to 60% of dengue cases [
12], efforts should be made to encourage testing even in the absence of symptoms. In particular, travelers from high-risk countries should be urged to undergo testing if they experienced mosquito bites, which could be facilitated by adding mosquito bite history as a required item on entry health declaration forms.
Notably, all 3 confirmed cases exhibited RDT band intensity at the level of moderately positive or higher (
Table 3;
Figure 2). Consistent with these findings, prior studies have demonstrated that stronger RDT intensity correlates with a higher probability of true positivity [
7]. A similar trend has been reported for severe acute respiratory syndrome coronavirus 2 rapid testing, where higher viral loads are associated with increased positivity rates [
13]. Conversely, all 7 cases with marginal RDT results tested negative on confirmatory testing (
Table 3). These outcomes may represent false positives, but it is also possible that the dengue incubation period was incomplete, particularly as most of these travelers had spent 5 days or fewer overseas, while the average incubation period of dengue is 5 to 7 days [
14]. Therefore, individuals with marginal results should be advised to undergo repeat testing if symptoms develop or worsen.
In the Republic of Korea, no cases of mosquito-borne dengue transmission have been reported to date, aside from a healthcare-associated needle-stick incident [
15,
16]. However, because
A. albopictus, a known vector for dengue, is widely distributed across the country, rapid responses are essential when confirmed cases are identified. To facilitate this, individuals with positive RDT results are instructed by quarantine officers to visit a public health center or hospital for confirmatory blood testing (
Figure 1). During the study period, however, one traveler with a strongly positive RDT result declined confirmatory testing, and the case was not pursued further (
Table 3). To prevent such losses to follow-up and ensure timely diagnosis, inter-agency coordination should be strengthened, including the option of directly transferring RDT-positive travelers from quarantine stations to designated medical institutions.
Delays in confirmatory testing were also observed. On average, confirmatory results required 4.00 days at hospitals and 2.71 days at public health centers (
Table 4). The longer delays at hospitals were largely attributable to scheduled specimen transport, whereas public health centers were able to send samples to public health laboratories immediately upon collection. Turnaround times were shorter for weekday arrivals (2.33 days) than for weekend arrivals (5.00 days), suggesting that reduced weekend operations contributed to delays. To address this, quarantine stations and public health centers may need to expand their capacity for blood sampling and confirmatory testing on weekends. Furthermore, travelers with positive RDT results should be advised to limit social activities until results are confirmed. Another approach to reduce delays would be to incorporate NS1 antigen detection by RDT into the confirmatory diagnostic criteria. Although current KDCA guidelines do not accept RDT results as confirmatory for dengue, the World Health Organization already recognizes NS1 antigen detection by RDT, along with ELISA, as acceptable diagnostic confirmation [
17]. If adopted, this policy would allow quarantine officers to issue a certificate of positivity at the point of entry—even on weekends—without requiring additional sample collection at medical institutions, thereby expediting treatment initiation. However, clear diagnostic criteria must be established to address the relatively high false-positive rate associated with RDT.
This study examined the characteristics and response processes of dengue cases detected early at a major port of entry. Nonetheless, the small sample size and retrospective design limited the scope of statistical analysis, and detailed information such as serotype identification was not available. Future studies with larger datasets are needed to improve the reliability and generalizability of these findings.
