qPCR indicates quantitative PCR; CSF, cerebrospinal fluid; ID, infectious diseases.
AHHV-6B DNA is typically detected in blood by PCR in patients with HHV-6B encephalitis. If the plasma or CSF HHV-6B viral load does not decrease >1 log10 copies/ml after ≥2 weeks of therapy or is persistently positive for ≥3 consecutive weeks, test for iciHHV-6.
BAny detection of HHV-6 species A or B DNA in CSF is considered abnormal. However, HHV-6 DNA can be detected in the CSF in the absence of clinical symptoms[17] or when the pre-test probability for HHV-6B encephalitis is low.[18] Close monitoring without treatment can be considered in select cases with the guidance of an ID consult. These recommendations are based on expert opinion and adapted from the 7th European Conference on Infections in Leukaemia (ECIL) 2017 guidelines.[58]