Kinetics and clinical significance of human herpesvirus 6 DNA shedding in saliva after allogeneic hematopoietic stem cell transplantation.

BACKGROUND Little is known about the kinetics and clinical significance of saliva human herpesvirus-6 (HHV-6) DNA after hematopoietic stem cell transplantation (HSCT). METHODS In this observational study, we quantified HHV-6 DNA in serially collected plasma and saliva from allogeneic HSCT recipients. Associations between the status of salivary HHV-6 DNA and the development of HHV-6 encephalitis, depression, and oral mucosal graft-versus-host disease (GVHD) were retrospectively analyzed. RESULTS A total of 787 plasma and 434 saliva samples were collected from 56 patients. The cumulative incidence of HHV-6 DNA in plasma and saliva at 60 days after transplantation was 51.8% and 83.9%, respectively. The peak level of salivary HHV-6 DNA was significantly higher in patients who displayed plasma HHV-6 DNA than in those who did not (median, 51,584 copies/mL versus 587 copies/mL; P<0.0001). Salivary HHV-6 DNA levels increased after positive plasma HHV-6 DNA was detected and remained high during observation period. Despite the frequent occurrence of positive salivary HHV-6 DNA, no patient developed depression. Positivity of salivary HHV-6 DNA was not significantly associated with the development of HHV-6 encephalitis (P=1.00, Fisher's exact test) or oral mucosal GVHD (P=0.71, Grey's test). No significant relationship between salivary HHV-6 DNA and these diseases was found even when comparing higher HHV-6 DNA loads in saliva. CONCLUSION Salivary HHV-6 DNA levels increased after HHV-6 DNA was detected in the blood. However, no epidemiological evidence was shown to support a role of salivary HHV-6 in the development of HHV-6 encephalitis, depression, and oral mucosal GVHD.