Transient versus persistent BK viremia and long-term outcomes after kidney and kidney-pancreas transplantation.

BACKGROUND AND OBJECTIVES The objective was to study the long-term impact of transient versus persistent BK viremia on kidney transplant outcomes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In total, 609 recipients who underwent kidney transplant from 2007 to 2011 were screened at months 1-12 for the occurrence of polyomavirus BK viremia; 130 patients (21.7%) developed BK viremia during the first year post-transplant. BK viremia patients were classified according to duration of infection (more or less than 3 months), and BK viral loads (more or less than 10,000 copies/ml) were classified as transient low viremia (n=42), transient high viremia (n=18), persistent low viremia (n=23), and persistent high viremia (n=47). All patients were followed a median of 36 (3-66) months. The rates of BK polyomavirus-associated nephropathy, acute rejection, and 1-year graft function were compared with the polyomavirus BK-negative control group. RESULTS Patient and graft survival were not significantly different among the groups. Graft function (creatinine; milligrams per deciliter) at 1 year was significantly worse in the persistent high viremia (1.75±0.6) and transient high viremia (1.85±0.7) groups compared with aviremic controls (1.47±0.4; P=0.01 and P=0.01, respectively). The incidence of BK polyomavirus-associated nephropathy was limited to the persistent high viremia group (1.3%, P<0.001). The transient high viremia (50%) and persistent high viremia (34%) groups showed significantly (P=0.01) increased incidence of acute rejection versus aviremic controls (21.5%), transient low viremia (19%), or persistent low viremia (17.3%) groups. CONCLUSION Low viral load BK viremia, either transient or persistent, was not associated with long-term transplant outcomes. Persistent high viremia was associated with a greater risk for BK polyomavirus-associated nephropathy and subsequent graft dysfunction. Although transient high viremia was not associated with BK polyomavirus-associated nephropathy, it was associated with worse graft function. These data support the role of surveillance for BK viremia after transplant.