*Purpose: BK viremia was a major cause of kidney transplant failure in the early 2000’s and remains a risk factor for subsequent rejection. The standard of care at our large transplant center now includes frequent testing for BK viremia and early reduction in immunosuppression. What are the features and outcomes of BK infection in the setting of aggressive monitoring and treatment?

*Methods: We retrospectively analyzed the demographics and outcomes of 401 renal transplant recipients with BK viremia from 2/2006 to 8/2017. Demographic data, transplant type and outcome, biopsy reports, and BK viremia tests were collected from electronic medical records and laboratory information systems. Demographic data was analyzed by chi-squared and Fisher exact tests, and survival data was analyzed by effect likelihood ratio. (JMP v15, SAS).

*Results: During the study period, there were roughly 2550 kidney transplants, corresponding to a 15.6% rate of BK viremia. Patients with BK viremia were of similar gender (253/401, 63.1% male) compared to the overall transplant population (62.2% male; p=0.74 by Fisher exact). 127 patients (31.7%) with BK viremia were non-white (97 African-American, 10 Asian, 20 Native American and other), similar to regional demographics. The proportion of living related (15.2%), living unrelated (23.9%), and deceased donor (60.8%) transplants were also similar to the overall transplant population (17.8%, 23.6%, and 58.6%; p=0.43 by chi-squared). In patients with BK viremia, there was no association between peak BK titer and risk of graft failure (p=0.93, likelihood ratio) or combined failure/death (p=0.98). Duration of BK infection correlated with better outcome (p=0.019 and 0.032), likely due to length bias. Graft half-life was similar for patients with BK viremia and nationally reported graft survival (deceased ~13 years, living ~16 years).

*Conclusions: Kidney transplant recipients with BK viremia are demographically similar to the overall transplant population. In comparison to historical reports, BK infection does not affect graft failure and overall survival in a modern, aggressively managed cohort. Within the cohort of patients with BK viremia, severe or persistent infections also do not predispose to poor outcome. There were 734 biopsies on 348 of the patients in the study during active BK viremia or within 6 months after viral clearance, and future studies will examine the influence of histologic features during and after infection on graft survival.

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