[Clinical characteristics of HHV-6 infection after allogeneic hematopoietic stem cell transplantation].

<b>Objective:</b> This study aimed to analyze the clinical manifestations of human herpesvirus 6 (HHV-6) infection within 100 days after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and to investigate the association of HHV-6 viral load with clinical outcomes as well as the effect of antiviral treatment on the course of HHV-6 infection. <b>Methods:</b> This retrospective study included patients who tested positive for HHV-6 within 100 days after allo-HSCT at the Peking University Institute of Hematology from February 2016 to February 2023. The study analyzed the patients' baseline characteristics, including age and transplantation type, as well as their clinical manifestations. Additionally, post-transplant complications were examined. <b>Results:</b> This study detected that 305 patients with HHV-6 infection were positive with a median time of 20 days post-transplant. Fifteen patients were asymptomatic, whereas the remaining patients exhibited the following symptoms: fever, rash, diarrhea, hemorrhagic cystitis, delayed platelet engraftment, central nervous system symptoms, abdominal pain, pneumonia and perioral numbness. Acute graft-versus-host disease (aGVHD) was diagnosed in 189 patients, with 45 cases of HHV-6 infection occurring before the onset of aGVHD and 120 cases occurring after aGVHD developed. Quantitative HHV-6 detection was available for 45 patients, and no statistically significant differences were found in the clinical manifestations according to the viral titer. A total of 108 (35.41%) patients experienced coactivation with other viruses, including cytomegalovirus, BK virus, and Epstein-Barr virus (EBV). Notably, coinfection with EBV was determined as an independent risk factor for overall survival (OS). No statistically significant difference in the time to HHV-6 viral clearance was observed between the antiviral treatment and non-treatment groups [7 (5-10) days <i>vs</i> 8 (4-14) days, <i>P</i>=0.199]. Similarly, the 5-year OS rates between the two groups were not significantly different [ (82.7 ± 2.6) % <i>vs</i> (91.3 ± 3.1) %, <i>χ</i>(2)=3.304, <i>P</i>=0.069]. <b>Discussion:</b> The most prevalent clinical manifestations were fever, rash, and diarrhea in patients with HHV-6 infection after allo-HSCT. No significant correlation was found between the severity of the clinical symptoms and the viral titer. Additionally, no significant differences in the time to HHV-6 clearance or 5-year OS were observed between patients who received antiviral treatment and those who did not.