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An emerging infectious disease, severe fever with thrombocytopenia syndrome (SFTS), was identified to be associated with a novel SFTS virus (SFTSV). Transmission of the disease among humans has been described, but clinical impact factors and transmission mechanisms still need further study. An outbreak of person-to-person transmission of SFTS in a cluster of nine patients that occurred in an SFTS endemic area, Penglai County, Shandong province, China, was investigated. We found that the onset date of all eight secondary SFTS patients ranged from 7 to 13 days after exposure to the corpse of the index patient, and clinical incubation time was mostly focused on 9-10 days (n = 6). The two dead patients, including the index patient and one secondary infected patient, presented unusually high levels of viral load (6 × 10(8-9) copies/mL), low levels of platelets count (<55 × 10(9)/L), and significant increase of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, and creatine kinase values in the second week, and died on day 10 or 11 after disease onset. Genetic sequencing revealed 100% homology among virus strains isolated from the index patient and five secondary patients. Risk factors assessment of the person-to-person transmission revealed that the major exposure factor was blood contact without personal protection equipment. Information from this study provided solid references of SFTS incubation time, clinical and laboratory parameters related to SFTS severity and outcome, and biosafety issues for preventing person-to-person transmission or nosocomial infection of SFTSV., (Copyright © 2014 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)

SFTS virus (SFTSV) is a novel bunyavirus that causes severe fever with thrombocytopenia syndrome (SFTS), an emerging infectious disease that occurred in China in recent years, with an average case fatality rate of 10-12%. Intervention in the early clinical stage is the most effective measure to reduce the mortality rate of disease. To elucidate the natural course of and immune mechanisms associated with the pathogenesis of SFTSV, 59 laboratory-confirmed SFTS patients in the acute phase, who were hospitalized between October 2010 and September 2011, were enrolled in this study, and the patients sera were dynamically collected and tested for SFTSV viral RNA load, 34 cytokines or chemokines and other related laboratory parameters. All clinical diagnostic factors in the acute phase of SFTS were evaluated and assessed. The study showed that the severity of the disease in 11 (18.6%) patients was associated with abdominal pain (p 0.007; OR = 21.95; 95% CI, 2.32-208.11) and gingival bleeding (p 0.001; OR=122.11; 95% CI, 6.41-2328). The IP-10, TNF-α, IL-6, IL-10, granzyme B and HSP70 levels were higher over the 7-8 days in severe cases, accompanied by altered AST, CK and LDH levels. HSP70 (p 0.012; OR=8.29; 95% CI, 1.58-43.40) was independently correlated with the severity of the early acute phase of SFTSV infection. The severity of SFTS can be predicted based on the presence of symptoms such as abdominal pain and gingival bleeding and on the level of HSP70 in the acute phase of the disease., (© 2014 The Authors Clinical Microbiology and Infection © 2014 European Society of Clinical Microbiology and Infectious Diseases.)