A cluster of BK polyomavirus-associated hemorrhagic cystitis after allogeneic hematopoietic stem cell transplantation

Background BK polyomavirus (BKV) can cause hemorrhagic cystitis (HC) in immunocompromised patients after hematopoietic stem cell transplantation (HSCT). It remains unclear whether nosocomial BKV infections occur. During a 9-month period, an increase in BKV-associated HC (BKV-HC) cases was observed at our institution. Aim The BKV-HC cluster population was compared with populations of HSCT patients from before and after the BKV-HC cluster to evaluate whether nosocomial BKV transmission had occurred. Methods A retrospective analysis was carried out to assess the risk of patients developing BKV-HC after HSCT. The background data of the cluster patients were compared with those of the patients who underwent HSCT before or after the cluster, and the collected BKV isolates were serotyped. Results BKV-HC involving grade >= 2 hematuria occurred in six of 15 HSCT recipients during a 9-month period. The incidence of BKV-HC was significantly higher in this period than in the other periods (p = 0.0014). There were no significant differences in the patients' background data between the cluster and non-cluster periods, including in terms of risk factors for BKV-HC. Serotype analyses of BKV revealed that the BKV detected in the urine samples from four of the six BKV-HC patients belonged to subtype Ic. The gene sequences of these four BKV exhibited >99.5% homology. Conclusion Our study suggests that nosocomial BKV infections may occur after HSCT. Although many cases of BKV-HC are caused by the reactivation of a latent virus, it is necessary to employ appropriate hygiene measures when cases of BKV-HC occur.