Clinical Feature And Prognosis Of 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 1s majorly transmitted by tick-borne bunyavirus.Sporadic reports suggested that SFTS could be transmitted among humans.However,clinical features and disease progression of secondary infection of SFTS have not been comprehensively characterized so fanMethods:A retrospective study of 90 SFTS patients was performed in a tertiary hospital of Nanjing,China,from Oct 2010 to Oct 2016,including 83 cases of primary SFTS and 7 cases of secondary SFTS.Exposure history and key event timeline for secondary patients were outlined.Results:7 secondary SFTS cases were infected SFTSV by human-to-human transmission.5 cases were transmitted by the index patient's blood,bloody secretion or body fluids with unprotected skin.2 cases acquired SFTSV infection by needle-stick injury.These secondary patients in our cohort did not have any prior history of tick bite or contact with livestock in recent two months.In contrast,among 83 primary SFTS cases,36.1%of patients confirmed to have tick bite prior illness onset.20.5%of them denied the history of tick bite,and the rest was not sure of tick bite history.None of them have contacted vsMth SFTS patients within 2 month before illness onset.20 out iof 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.Notably,none of secondary patients,but a large portion of primary SFTS patients developed diarrhea and lymphadenopathy.Moreover,hemorrhagic signs,central nervous system(CNS)symptoms and MODS were present in a considerable portion of primaxy SFTS cases,but none in secondary patients.The natural history of SFTS is divided into three distinct stages:fever,MODS,and convalescence,whereas none of secondary SFTS patients proceeded to the stage of MODS.At day 7-13,the mean viral load of primary and secondary patients was 5.40±1.56 log10 copies/mL and 3.73±0.90 log10 copies/mL,respectively(p=0.03).Conclusion:Secondary SFTS infection acquired by human-to-human transmission usually leads minor clinical representations and superior prognosis compared to primary SFTS infection,suggesting that the transmission route makes a difference in pathogenesis and clinical outcome of SFTS disease.