Melioidosis, as also called Whitmore’s disease, is a zoonosis that can infect humans or animals. Melioidosis, which is infection with the gram-negative bacterium Burkholder pseudomallei, which found in contaminated soil and water [1-7]. It is spread to humans and animals through direct contact. As a pollutant, it is widely distributed in endemic regions of the tropics and subtropics. Northern Australia and Southeast Asia, including Thailand, Malaysia, Indonesia Cambodia, Philippines, Laos, Vietnam, and Singapore, etc. [1-11]. It can occur through contact with the blood or bodily fluids of an infected person, especially if aerosols are generated during the procedure. Following the initial recognition of melioidosis by the British pathologist Alfred Wrinkled Whitmore and his Indian assistant, CS Krishnawami in 1911 have been reported [3]. The bacteria that cause melioidosis usually enter the body through inhalation of soil dust or water droplets, contact with contaminated soil through breaks on the skin, or by ingestion of contaminated water. It is person-to-person transmission is very rare, but can occur through contact with blood or body fluids of an infected person, especially if procedures produce aerosols [1-7]. Symptoms that can cause a person to be infected depend on the location of infection. For example, some people might not experience any symptoms. In case of local infection, skin sores are characterized by pain, swelling, heat, ulcers, or abscesses in a specific area. Symptoms of lung infection include cough, chest pain, fever, headache, or loss of appetite. Other symptoms include fever, weight loss, and stomach or chest pain, muscle or joint pain, and seizures, etc. [1-11].

In Korea (Republic of) and Japan are not endemic regions for melioidosis; however, infections among oversea travelers are being reported [6,7,12,13].

In the present study, we investigated the epidemiological aspects and status of imported melioidosis infection cases in Korea and Japan during 2011-2020. In the cases of both Korea and Japan, no indigenous melioidosis cases have been confirmed, and all reported cases were diagnosed in travelers or immigration from endemic or epidemic countries [1-3]. Considering this situation, in Korea the Infectious Disease Control and Prevention Act classified human melioidosis among group III notifiable infectious diseases by the Korea Diseases Control and Prevention Agency (KDCA) [12]. Japan’s Infectious Disease Control Law also has classified human melioidosis cases a category IV notifiable infectious disease by the National Institute of Infectious Diseases (NIID), Japan [13].

In this study, trends in the epidemiological aspects of imported melioidosis cases among oversea travelers between Korea and Japan during the period from 2011 to 2020 were investigated.

We investigated raw data of 26 melioidosis cases among overseas travelers (OTs) in Korea during 2011 to 2020, which were obtained from the National Notifiable Infectious Disease Report on the KDCA [12]. Data of 14 melioidosis cases in Japan during the same period were obtained from Annual Surveillance Data and the Infectious Diseases Weekly Report, both available on the Infectious Diseases Surveillance center and the NIID [13]. This study was exempted from institutional review board review as it was a retrospective data study.

To better quantify the impact of melioidosis infections in Korea and Japan, we compiled and analyzed that the cumulative incidence rate (CIR) per 1,000,000 in OTs, and related risk factors such as sex, male-to-female morbidity ratio (MFMR), adjusted-age groups, seasonality distribution of cases, and the presumptive origin of melioidosis etc., respectively. Finally, statistical analysis was performed using Excel 2010 statistical software (Microsoft). The Chi-square test or paired t-test was used to assess whether differences according to each variable are statistically associated. The result was considered to be statistically significant for P-value less than <0.05.

We observed that the trends in the epidemiological aspects of melioidosis infection cases among oversea travelers between Korea and Japan during the period from 2011 to 2020 were analyzed under five heading as Table 1 follows; the CIR, sex, age, seasonality, and the regions presumptive original of melioidosis infections, etc., respectively. There was a total of 26 cases of melioidosis infection in Korea, and total 14 cases in Japan between 2011 and 2020. CIR per 1,000,000 OTs in Korea (0.14) that statistically did not substantially differ from that in Japan (0.09).

On the other hands, we observed the melioidosis of male (96.2% of total 26 cases) were much more than that for female (3.8% of total 26 cases) in OTs of Korea (P<0.01), while there was significant differences level between males (85.7% of total 14 cases) and females (14.3% of total 14 cases) in OTs of Japan (P<0.01).

We utilized the MFMR to estimate and compare of melioidosis infections between Korea and Japan. MFMRs were 25.0 in Korea and 6.0 in Japan.

When we classification of the total 26 of melioidosis cases in Korea by the groups were as follows that the age-adjusted groups of under 19, 20-39, 40-59, and over 60 years old that the percentage were 0%, 7.7%, 46.15%, and 46.15%, respectively (P<0.01), and those of the total 14 cases for Japan were 0%, 21.4%, 28.6%, and 50.0%, respectively (P<0.01). The distributions by age-adjusted groups were similar in Korea and Japan that the total cases much occurred the over 40-years-old age groups bracket, clearly showing a higher incidence (P<0.05).

The estimation for the seasonal pattern of the total 26 imported melioidosis infection cases in Korea from 2011 to 2020 were 23.1% in spring, 38.4% in summer, and 23.1% in autumn, and 15.4% in winter, respectively. During the same period of Japan were total 14 cases of melioidosis were 14.3% in spring, 50.0% in summer, 21.4% in autumn, and 14.3% in winter, respectively. It is shows in Table 1 and Fig. 1 as follows that the year-round distributions of melioidosis infection cases were found to be more frequent in summer in Korean and Japanese.

There was a total of 26 cases of melioidosis infection in Korea, and that of total 14 cases in Japan between 2011 and 2020. Statistically, CIR per 1,000,000 OTs in Korea (0.14) was not significantly different from that in Japan (0.09). In the case of these data suggest people from Korea engage in oversea travelers to the presumptive origins of melioidosis endemic areas in more than those from Japan in the same period [8,12-15].

We utilized the MFMR to estimate and compare of melioidosis infections between Korea and Japan. MFMRs were 25.0 in Korea and 6.0 in Japan. These data may represent a difference in activities associated with exposure in possible origins of melioidosis infections between men and women in the travel destinations [12-15].

The distributions by age-adjusted groups were similar in Korea and Japan that the total cases much occurred the over 40-years-old age groups bracket, clearly showing a higher incidence (P<0.05). These data were strongly suggested that the melioidosis infections among OTs who are occurred of the business or vacation of the prime of life in Korea and Japan [1-11].

We analyzed the seasonal pattern of the imported melioidosis infection cases in Korea and Japan. These data strongly indicate that the imported melioidosis infections cases in these two countries influenced by their summer vacation seasons or visit for business, and that the facts of case distribution of melioidosis cases outbreaks may be due to the season and environmental conditions by the destination [1-11].

We have an information that the presumptive origin of imported melioidosis of the total 26 cases in Korea by the KDCA [8] between 2011 and 2020 were as follows; Thailand (38.5%), Cambodia and Vietnam (each as 23.1%), Philippines (7.7%), and Indonesia and Singapore (each as 3.8%), etc. respectively. Moreover, we observed that these data strongly indicate (Table 2) that melioidosis infection cases is influenced by their peculiar conditions that Koreans tend to travel to developing Asian countries [1-11], where the risk for melioidosis is significantly higher than in other countries. The most frequently suspected region as the origin of infection was Southeast Asia. Therefore, imported melioidosis infection is influenced by travel destination [1-7]. In recent years, OTs in both Korea and Japan are showing greater tendency to visit developing countries in Asia, where risk of melioidosis infection is substantially higher than in developed countries [1-7]. Furthermore, melioidosis endemic area not limited to rural area of such countries. As the habitat has expanded into the urban residential areas that travelers prefer to visit, the endemic is spreading to urban areas [1-11].

The number of melioidosis cases reported in Korea and Japan is a reminder of the need for target prevention strategies, early disease recognition and treatment, and sustainable surveillance systems. We observed and analyzed raw data on melioidosis infection between 2011 and 2020 disproportionately higher incidence among OTs. Findings of these epidemiological aspects of national surveillance data could be useful in defining demographics, distribution, and trends in melioidosis infection.

We observed that there is a similar pattern of epidemiological aspects of melioidosis infection cases in Korea and Japan. These results underscore the ongoing emergency of melioidosis and provide a basis for targeting prevention campaigns to population with increasing incidence. Travelers and air crews traveling to meliodosis endemic area such as Southeast Asia could be at risk of melioidosis infection. It would be wearing personal protective equipment such as waterproof boots and gloves to prevent contact with soil and water will help to reduce the possibility of infection [1-5]. Moreover, we hope that this information will be a useful reference in the further study of melioidosis in Korea and Japan.

We thank for the raw data of imported melioidosis infection cases used in this study by the KDCA and the NIID of Japan.

No potential conflict of interest relevant to this article was reported.

Conceptualization: all authors. Data curative: all authors. Analysis and interpretation: all authors. Writing the original draft: all authors. Critical revision of the article: all authors. Final approval of the article: all authors. Overall responsibility: all authors.