Isolated heart and liver transplant recipients are at low risk for polyomavirus BKV nephropathy

Background: BKV infection and nephropathy is a significant cause of allograft dysfunction in kidney transplantation. BKV viremia, rather than viruria, corresponds to BKV nephropathy. The prevalence of BKV viremia in non-renal solid organ transplants has not been systematically evaluated. Methods: We determined prevalence of BKV viremia in kidney, combined kidney-heart, kidney-liver, kidney-pancreas, kidney-heart-liver, and heart and liver transplant recipients using BKV-PCR. Results: Seven out of 173 (4%) kidney transplant recipients had BKV viremia, with BKV > 2 x 10(5) copies/mL in 6/7 and 1.9 x 10(3) in the remaining one patient. BKV viremia was not found in 24 heart transplant recipients, whereas 1/37 (2.7%) liver transplants showed low copy numbers (<= 10(3)). BKV-PCR <= 10(3) copies/mL were also found in one of each combined kidney-heart and kidney-liver transplant recipients. BKV nephropathy was proven by biopsy in 4/6 patients with high BKV viral loads. All six patients showed renal dysfunction, requiring reduction in immunosuppression and antiviral therapy. All four patients with low BKV viral loads (1.9 x 10(3) or <= 10(3)) showed stable renal function after reduction of immunosuppression or no treatment, respectively. Conclusion: Higher BKV levels in plasma are associated with renal dysfunction. Kidney transplant recipients are at high risk compared with recipients of isolated heart or liver allografts, for development of BKV nephropathy.