Introduction
BK virus (BKV) is a member of the polyomavirus family, which was first isolated in 1971 from the urine sample of a renal transplant patient, with clinical observations made over the years, it was understood that BKV is responsible for BKV nephropathy (BKVN) (1-3). The exact prevalence of BKVN is not known, however, it is estimated to be in the range of 1-15 %. BKVN is an important clinical problem causing graft loss in 15-50 % of transplant patients (4). Risk factors for BKV are aggressive immunosuppression, high human leukocyte antigen (HLA) mismatch, ureteral stent use, rejection therapy, prolonged ischemia duration, advanced age, male recipient, diabetes mellitus (DM), lymphocyte depleting induction therapies, tacrolimus, and mycophenolate- based regimens (5-10). It has been shown that the use of double-J-Stent (DJS) in experimental animal models causes superficial epithelial destruction, ulceration, and inflammatory changes on the transitional epithelium in rat ureters, as well as increasing the incidence of BKVN by 4 times (2,11-13). Studies have shown that conditions that cause persistent hydronephroses, such as posttransplant ureter flexion and ureteral stenosis, may play a dynamic role in the pathogenesis of polyoma virus-associated nephropathy by causing ureteral reflux. Vesicoureteral reflux (VUR) may occur with normal bladder contraction while using DJS (14,15). In 2015, we compared the patients with anti-reflux mechanism DJS (ARD-DJS) and those used standard DJS (st-DJS) in terms of BKV and BKVN frequency in 90 kidney transplant patients in two centers (Figure 1). In this study, BKV was observed with significantly less frequency in univariate analyzes in patients with ARD-DJS. However, no significant difference was observed in the multivariate analyzes. In this study, the small number of cases and the short follow-up duration were the factors limiting our study (13). With the increase in the number of our patients over time and lengthening of the follow-up duration, we needed to re-evaluate the data in one center.