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BACKGROUND: The significance of JC polyomavirus (JCPyV) after kidney transplantation ranges from irrelevant to full-blown nephropathy or PML. OBJECTIVES: To investigate the clinical significance of high-level JCPyV viruria and JCPyV primary infections after kidney transplantation. STUDY DESIGN: JCPyV viruria was detected in routine screening by quantitative real-time PCR in 40/238 kidney transplant recipients and was high-level (<107 copies/ml) in 17 patients. A protocol biopsy at the time of JCPyV viruria was available from 10 patients. RESULTS: Peak urine viral loads were 1.0x107-2.5x109 copies/ml in the 17 high-level viruria patients. 6/15 (40%) patients with high-level JCPyV viruria with pretransplant sera available were JCPyV IgG negative suggesting that JCPyV viruria resulted from the donor graft in most cases. No acute graft dysfunction was associated with JCPyV viruria. No positive SV40 staining was detected in protocol biopsies, and no specific histopathology was associated with high-level viruria; JCPyV nephropathy was not found. No differences were seen in histopathology or graft function at 3 years in patients with high-level viruria compared to non-JCPyV viruric patients transplanted during the same time period, and outcome was similar in patients with presumably primary and reactivated JCPyV. The mean estimated GFR at last follow-up was 44ml/min (range 12-60ml/min). One graft with high-level viruria was lost 9 years posttransplant due to recurrent IgA nephropathy CONCLUSIONS: High-level JCPyV viruria seems to be associated with primary JCPyV infection reflecting the average seroprevalence of 60%, but is not stringently associated with inferior graft function or survival, or histopathological changes.
