High incidence of BK virus‐associated hemorrhagic cystitis in children after second or third allogeneic hematopoietic stem cell transplantation

BKV ‐ HC is a serious complication of allogeneic HSCT . To characterize the incidence, risk factors, and clinical outcomes of post‐ HSCT BKV ‐ HC , we retrospectively analyzed 112 patients who underwent one or more allogeneic HSCT s at our hospital between 2001 and 2017. Twenty underwent second or third HSCT thereafter. Ten patients developed BKV ‐ HC at a median of 30 days after HSCT . The 100‐day cumulative incidences of grade 0‐4 and grade 2‐4 BKV ‐ HC were 7.8% and 6.2%, respectively. HSCT s performed in 2011‐2017 associated with significantly higher 100‐day cumulative incidence of grade 2‐4 BKV ‐ HC (14.0%) than HSCT s performed in 2001‐2010 (1.3%, P  =   0.004). On multivariate analysis, second or third HSCT was the only independent significant risk factor for development of grade 2‐4 BKV ‐ HC ( P  =   0.015). Serial PCR monitoring of urine and blood BKV load did not predict BKV ‐ HC . The recent increase in the incidence of BKV ‐ HC may reflect recent innovations in transplant technologies that facilitate second or third HSCT , which are known to cause prolonged immune deficiency. If safe and effective treatment or prophylaxis becomes available, it could be used to target the high‐risk patients for BKV ‐ HC .