Characterization of clinical features and outcome for human-to-human transmitted severe fever with thrombocytopenia syndrome

Background: Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease identified in 2009. SFTS is mainly transmitted by contact with ticks or animals; however, sporadic reports suggested that SFTS could be transmitted among humans.Objectives: We aimed to comprehensively characterize clinical features and disease progression of SFTS acquired by human-to-human transmission.Study design: A retrospective study of 90 SFTS patients was performed in a tertiary hospital of Nanjing, China, from October 2010 to October 2016. Seven cases of secondary SFTS were identified based on their epidemic timeline. Their clinical presentations, dynamic laboratory results and clinical outcome were analyzed.Results: First, 20 out of 83 primary SFTS patients were deceased, leading to a case-fatality ratio of 24.1%, while all secondary patients survived, suggesting a superior clinical outcome for secondary infection. Moreover, clinical symptoms and laboratory tests in primary and secondary SFTS patients were analyzed, respectively. Secondary SFTS patients developed milder clinical manifestation in the absence of neurological disorder and multiple organ failure. Further, clinical laboratory tests revealed that secondary patients had less disturbed key laboratory parameters, compared to those in primary SFTS patients. During day 7–13 post illness onset, most of the clinical laboratory results of secondary patients went back to normal range. They also had significantly lower level of viral load than primary patients.Conclusions: Secondary SFTS acquired through human-to-human transmission leads to milder clinical representations and superior prognoses compared to primary SFTS, suggesting that the transmission route makes a difference in disease progression and clinical outcome of SFTS disease.