The prospective evaluation of viral loads in patients with severe fever with thrombocytopenia syndrome.

Background: Severe fever with thrombocytopenia syndrome (SFTS), caused by novel bunyavirus (SFTSV) is a potentially fatal disease that was first identified in China. Person to person transmission through contact with blood or body fluids was considered as an important infection route.

Objectives: The study is designed to investigate the longitudinal viral loads following SFTSV infection and to identify factors affecting viral shedding in SFTS patients.

Methods: A prospective, observational study was performed on 208 laboratory-confirmed SFTSV infected patients in Xinyang, Henan Province. Sequential serum samples were collected on admission and during the hospitalization for quantification of SFTSV RNA by real-time RT-PCR.

Results: The viral RNA was undetectable in 55.6% of the patients on admission into the hospital, becoming detectable in most cases until three days and attained maximum level on six days after disease onset. This was followed by an obvious decrease thereafter, but maintained detectable for over 20 days. Viral load was independently predictable of severe disease outcome throughout the hospitalization. Viral load of >10(7)copies/mL was predictable of fatal outcome. The serum levels of PLT, WBC, LDH, AST and CK were significantly associated with viral loads level.

Conclusions: The diagnosis of SFTSV infection based on PCR test should be performed at least three days after disease onset. Peaking viral loads were attained around six days after disease, posing a highest risk of human-to-human transmission.