High infection rates and risk-adapted prevention strategies in contemporary pediatric allogeneic hematopoietic stem cell transplantation.

With recent changes in hematopoietic stem cell transplantation (HSCT) practices, such as the increasing use of alternative donors and ex vivo T-cell depletion, how various risk factors interplay and affect the timeline of infections have not been well elucidated. We retrospectively reviewed the first 100 consecutive HSCT from April 2019 to October 2021 in the only pediatric HSCT center in Hong Kong. We found that the vast majority of the allogeneic transplant recipients (69/74, 93.2%) had infections after HSCT, amongst which bacterial, viral, and fungal infection rates were 35.1%, 90.5%, and 9.5%, respectively. In contrast, only 30.8% (8/26) of autologous transplant recipients had infections (rate of bacterial, viral, and fungal infection were 19.2%, 15.4%, and 3.8%, respectively). Human herpesvirus 6 (HHV-6) and BK virus (BKV) typically occurred early after HSCT, adenovirus (ADV) and varicella zoster virus (VZV) thereafter, and cytomegalovirus (CMV) and Epstein-Barr virus (EBV) throughout the entire 2.5-year observation period. Ex vivo T-cell depletion was a general risk factor for viral infection with HHV-6 (hazard ratio [HR] = 3.03), BKV (HR = 3.36), CMV (HR = 4.45), and EBV (HR = 7.15); all