[BK virus infection in a child after an hematopoietic stem cell transplantation].

Polyomavirus hominis 1, better known as BK virus (BKV), infects up to 90% of the general population. Significant clinical manifestations can be seen in immunocompromised patients. We report a case of haemorragic cystitis likely due to BKV in a child after allotransplantation of hematopoietic stem cells. A 10-year old boy with poor-prognosis acute T lymphoblastic leukaemia underwent cord blood allogeneic stem cell transplantation while in his first relapse. Macroscopic haematuria and low back pain occurred by day 95, in the context of acute graft versus host disease and pulmonary aspergillosis. Histopathologic examination showed a cytopathogenetic effect consistent with the diagnosis of BKV infection. Urinary PCR was positive for BKV. Treatment with cidofovir was followed by a marked improvement of urinary symptoms. The current understanding, diagnosis, and treatment of BKV-associated infection is discussed.