[Infectious causes and management of Japanese spotted fever and severe fever thrombocytopenia syndrome in Ehime prefecture]

Objectives We investigated the infectious causes and management of Japanese spotted fever (JSF) and severe fever thrombocytopenia syndrome (SFTS), which are usually tick-borne infections, at a public health center in Ehime prefecture.Methods The doctor diagnosing JSF and SFTS at the public health center reported the infectious cases using the questionnaire based on the Ehime Epidemiological Surveillance of Infectious Diseases Program.Results There were 91 cases of JSF reported from August 2003, accounting for 56.5% of the whole Ehime prefecture. Since 67.0% of the JSF patients resided near the mountains with citrus cultivations, there were high chances of contact with ticks during farm work or their daily routine even if they did not visit the mountain areas. The distribution of the occupations of the JSF patients was as follows: citrus cultivator, 31.9%; farmer, 14.3%; and retired, 26.4%. The incidence of various clinical symptoms in the JSF patients was as follows: fever and systemic erythema, 100%; tick bite, 73.6%; liver dysfunction, 69.2%; disseminated intravascular coagulation (DIC), 14.3%; and neurological symptoms, 11.0%. The mortality rate was 1.1%. The incidence of DIC, which was considered a severe condition, was significantly low in patients with confirmed tick bites. There were 14 cases of SFTS reported from December 2013, accounting for 42.4% of the whole Ehime prefecture. Notably, 85.7% of the SFTS patients resided in the mountains. Moreover, 85.7% of the SFTS patients were retired. The incidence of various clinical symptoms in the SFTS patients was as follows: fever and marked leucopenia and thrombocytopenia, 100%; tick bite, 57.1%; diarrhea, 71.4%; neurological symptoms, 57.1%; and bleeding tendency, 42.9%. The mortality rate was 35.7%, and the average number of days from onset to death was 11.2 days.Conclusion Since this region is one of the leading citrus producing areas in Ehime prefecture, JSF is considered an occupational disease. It is frequently caused by tick bites while working in the mountain areas of citrus cultivations. Hence, citrus growers should be cautious of tick-borne infections. Recently, the number of JSF cases has been gradually decreasing due to awareness and education of the inhabitants. Currently, SFTS is considered a category IV infection disease, but it can rapidly lead to death after the onset of hemophagocytic syndrome. Therefore, doctors should immediately transfer the patients diagnosed with SFTS to a hospital with an intensive care unit.