Severe Fever with Thrombocytopenia Syndrome in South Korea, 2013-2015

Abstract

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was recently identified in China, South Korea and Japan. The objective of the study was to evaluate the epidemiologic and clinical characteristics of SFTS in South Korea.

Methods/principal findings: SFTS is a reportable disease in South Korea. We included all SFTS cases reported to the Korea Centers for Disease Control and Prevention (KCDC) from January 2013 to December 2015. Clinical information was gathered by reviewing medical records, and epidemiologic characteristics were analyzed using both KCDC surveillance data and patient medical records. Risk factors for mortality in patients with SFTS were assessed. A total of 172 SFTS cases were reported during the study period. SFTS occurred throughout the country, except in urban areas. Hilly areas in the eastern and southeastern regions and Jeju island (incidence, 1.26 cases /105 person-years) were the main endemic areas. The yearly incidence increased from 36 cases in 2013 to 81 cases in 2015. Most cases occurred from May to October. The overall case fatality ratio was 32.6%. The clinical progression was similar to the 3 phases reported in China: fever, multi-organ dysfunction, and convalescence. Confusion, elevated C-reactive protein, and prolonged activated partial thromboplastin times were associated with mortality in patients with SFTS. Two outbreaks of nosocomial SFTS transmission were observed.

Conclusions: SFTS is an endemic disease in South Korea, with a nationwide distribution and a high case-fatality ratio. Confusion, elevated levels of C-reactive protein, and prolonged activated partial thromboplastin times were associated with mortality in patients with SFTS.

Fig 1. Temporal distribution of 172 patients with severe fever with thrombocytopenia syndrome (SFTS) in South Korea, 2013–2015.

The main epidemic period of SFTS was May to October. No cases were reported from December to March, which is the winter season.

Fig 2. Geographic distribution of 172 patients with severe fever with thrombocytopenia syndrome (SFTS) in South Korea, 2013–2015.

SFTS occurred throughout the country with the exception of urban areas. The incidence was relatively low in the western and southwestern rice field areas and the scarcely populated eastern mountainous areas. Hilly areas were the major endemic regions. Orange circles indicate the site of infection, and the size of the circle represents the number of SFTS cases by area. Shading indicates cases per 100,000 persons.

Fig 3. Changes in laboratory parameters over time by intervals of 3 days in 120 patients with severe fever with thrombocytopenia syndrome.

The Y-axis values denote the mean and 95% confidence intervals. Blue and red lines indicate the non-fatal and fatal groups, respectively. The number in parenthesis shows non-fatal (blue) and fatal (red) patients included in the analysis at each time point. P values show the statistical significance of variables at each time point over 3 weeks between the two groups. WBC, white blood cell; Hb, hemoglobin; ALP, serum alkaline phosphatase; AST, serum aspartate aminotransferase; ALT, serum alanine aminotransferase; PT, prothrombin time; aPTT, activated partial thromboplastin time; CRP, C-reactive protein.