Seroprevalence and Factors Associated with Scrub Typhus Infection among Forestry Workers in National Park Offices in South Korea

Scrub typhus is caused by the arthropod-borne bacterium Orientia tsutsugamushi and is an endemic infectious disease in the Asia-Pacific area. This study aimed to investigate the seroprevalence of scrub typhus and identify associated risk and protective factors among forestry workers, a neglected risk group for scrub typhus, in National Park Offices in South Korea. A nationwide cross-sectional serosurvey was carried out on 1945 National Park Office forestry workers (NPOFWs) in South Korea during December 2016. We visited 29 main offices and used a structured questionnaire to collect data regarding general characteristics, work activities, work hygiene-related factors, and other potential risk factors. Serum samples from NPOFWs were tested using indirect immunofluorescence assay to detect O. tsutsugamushi immunoglobulin (Ig) G and M antibodies. Of the 1945 NPOFWs, 718 (36.9%) participated in this cross-sectional study. The seroprevalence, defined as >= 1:256 for IgG and/or >= 1:16 for IgM, was 4.9% (35/718). In multivariate logistic analysis, longer duration of work in national parks (>= 15 years; odds ratio (OR), 4.19; 95% confidence interval (CI), 1.71-10.28) and dry field farming (OR, 2.47; 95% CI, 1.12-5.46) were significantly associated with a higher risk of scrub typhus infection. Furthermore, the risk of scrub typhus infection was significantly lower among NPOFWs who washed working clothes daily (OR, 0.37; 95% CI, 0.18-0.75). This study indicated that scrub typhus is an important disease among NPOFWs in South Korea. Work hygiene, especially washing working clothes daily, needs to be emphasized among NPOFWs. Additionally, more precautions are required to diminish the rate of scrub typhus infection among NPOFWs who perform dry field farming.