BK virus infection in kidney transplant recipients

INTRODUCTION: Nephropathy associated with the polyomavirus type BK virus (BKV) has emerged as a cause of allograft failure linked to immunosuppressive regimens containing tacrolimus or mycophenolate mofetil (MMF). The outcome in BKV nephropathy is generally unfavorable, namely 50% of patients lose graft function. We herein report nine cases of BKV nephropathy after kidney transplantation. METHODS: From October 1998 to May 2003, 138 of 169 consecutive kidney transplant patients received tacrolimus-based immunosuppression, and 31 received cyclosporine-based immunosuppression. Additionally, 88.2% of the patients received mycophenolate mofetil (MMF). The diagnosis of BK infection was made by the presence of decoy cells in the urine and by allograft biopsy. RESULTS: There were nine cases of BKV nephropathy in kidney transplant recipients, an incidence of 5.3%. All patients with BKV nephropathy received tacrolimus, MMF, and steroids. The median time to diagnosis of BKV infection was 7.8 months after transplantation. All patients experienced an elevated serum creatinine, which stabilized or decreased in seven patients with altered or decreased immunosuppression. After a mean follow-up of 11.1 months, 2 (22.2%) of nine patients lost the graft. CONCLUSION: Because BKV nephropathy is a rare but serious complication after kidney transplantation, it should be included in the clinical differential of transplant dysfunction. In the absence of documented antiviral treatment, early diagnosis and judicious use of immunosuppressive agents is indicated to minimize the occurrence of BKV infection.