Objective: to evaluate the incidence of Betapolyomavirus hominis in individuals at risk of developing infectious complications associated with virus reactivation. Materials and methods. The prospective study included 601 patients in 6 groups: hematopoietic stem cell recipients with and without established hemorrhagic cystitis, allogeneic kidney recipients, HIV-infected persons, pregnant women and a control group. Quantification of B.hominis DNA by RT PCR was performed for 1202 samples of whole venous blood and urine. The results were statistically processed using the STATTECH program. Results. The prevalence of B.hominis among people at risk of developing infectious complications ranged from 6.0% to 89.2%, depending on the study group. Allo-HSCT recipients had the highest incidence of the viral DNA presence in urine samples – 89.2% with hemorrhagic cystitis and 26.3% without it, at concentrations up to 9.3×1011 IU/ml. In the remaining groups, the viral load in urine was lower (up to 1.1×108 IU/ ml), and the detection rate was: pregnant women – 14.3%, HIV-infected persons – 10.6%, allogeneic kidney recipients – 6.0%, control group – 5.8%. The chance of detecting viral DNA in urine samples of allo-HSCT recipients with hemorrhagic cystitis is 134.7 times higher than in the control group (p<0.001). B.hominis DNA was found in whole venous blood samples: 8.4% and 21.1% of allo-HSCT recipients with and without hemorrhagic cystitis, respectively (р=0,051), HIV– infected persons – 1.4%, control group – 0.4%. Simultaneous detection of viral DNA in blood and urine presented in patients after allo-HSCT, regardless of the presence of hemorrhagic cystitis and HIV–infected persons. Conclusion. Reactivation of B.hominis continues to pose a threat to human health and life, causing various complications in patients with weakened immune systems. The obtained data on the prevalence of B.hominis are necessary for studying the diseases associated with the virus and generating an algorithm for examining patients at risk of developing infectious complications. © 2025 Elsevier B.V., All rights reserved.