Introduction: The BK virus, belonging to the polyomavirus family, was first described in 1971 in a kidney transplant with ureteral stenosis, which eliminated cells with atypical nuclear morphology in the urine, and the name of the virus was established by the initials of the patient. Primary BK virus infection usually occurs in the first decade of life. After it, the virus colonizes the urinary tract and remains dormant in kidney cells. When immunity declines, the virus begins to replicate in the epithelial cells of the kidney, ureter, and bladder. In kidney transplantation, it can lead to the development of nephropathy and graft loss.

Materials and Methods: Observational, descriptive cross-sectional study. A review of a population of kidney transplant patients from living and cadaveric donors, over 18 years of age was made. 66 patients from whom quantitative polyomavirus BK-DNA viral load in plasma and urine was requested for a clinical indication from 2019 to 2022 were selected. Clinical, analytical, demographic, gender, type of transplant, and record of results variables were collected.

Results: Of 66 patients who were asked to have quantitative BK-DNA polyomavirus in plasma and urine, 23 patients tested positive for BK-DNA virus in plasma or urine, 82% were male, 56% were living donor patients, the debut mean VBK was at 48+/- 29.36 months. Of these 23 patients, 26% had a positive result only in urine and the rest in plasma and urine, 26% had impaired kidney function and the rest had stable kidney function from diagnosis to the present time, 2 patients had acute humoral rejection at the same time and one recurrence of his underlying glomerular disease. Of the patients who maintained stable renal function values, all had decreased immunosuppression, 14 patients were switched from tacrolimus to cyclosporine and 1 to mtor.

Conclusion: Early diagnosis of the infection alerts us to decreased immunosuppression, however, when concomitant rejection is associated, management can be more complicated. It is important to establish a screening protocol in transplant centers and to suspect this infection if there are symptoms or deterioration of renal function.