Phylogenetically proved BK virus-associated hemorrhagic cystitis outbreak among pediatric hematopoietic stem cell recipients

Objective: BK virus-associated hemorrhagic cystitis (BKV-HC) still remains as a life-threatening complication after Hematopoietic Stem Cell transplantation (HSCT). The origin of the virus was proposed as reactivation for a very long time and recently it is doubted to be a nosocomial transmission. In this study, we analyzed a possible nosocomial transmission of BK virus (BKV) in a pediatric HSCT clinic. Method: A variable region encompassing partial parts of VP1, VP2 and VP3 coding sequences and approximately 677 base pairs in length was sequenced with Sanger's dideoxynucleotide determination method. Then the sequenced region was phylogenetically analyzed. Results: All the information of 131 patients who had HSCT in Akdeniz University Hospital pediatric HSCT clinic between July 2019 and July 2022 were screened for BKV-HC. Twenty-six patients had BKV-HC and18 of them were related to an epidemic. Twenty patients including 16 pediatric and 4 adult HSCT patients were phylogenetically investigated. All the patients had BKV DNA positivity in the urine samples and 17 of them also had BKV-HC. Although 3 patients have BKV-DNA in the urine samples, they didn't develop HC. Conclusion: After alignment and phylogenetic analysis of the sequences, 3 clusters including 12, 3, and 2 patients having the same sequences were formed. To our knowledge, this is the biggest BKV-HC epidemic seen among HSCT patients. Also, nosocomial transmission affecting the most patients was proved with phylogenetic analysis. Key words: BKV, hemorrhagic cystitis, hematopoietic stem cell transplantation