Polyomavirus infection in pediatric renal transplant recipients: evaluation using a quantitative real-time PCR technique.

Polyomavirus infection and related nephropathy is being increasingly recognized as an important cause of allograft dysfunction in adult renal transplant recipients. We prospectively monitored pediatric renal transplant recipients for the presence of BK and JC polyomavirus in urine and blood using a quantitative PCR assay to evaluate the prevalence and clinical relevance of polyomavirus infection in the pediatric renal transplant population. Of 46 pediatric renal recipients who were evaluated, nine (20%) demonstrated isolated BKV viruria, while five (11%) had concomitant BKV viremia and viruria. JCV viruria was found in eight (17%) patients. BKV viremia was associated with a significantly higher urinary BKV viral load: median urinary viral load 1.9 x 10(9) copies/mL (range 6.7 x 10(2)-1.8 x 10(11)) for the group with concomitant viremia and viruria vs. 1.8 x 10(3) copies/mL (range 2.5 x 10(2)-4.5 x 10(6)) for the group with isolated viruria (p < 0.0001). In children that were followed prospectively since their transplantation, the BKV urinary viral load increased markedly before viremia became detectable a few weeks later. None of the patients with JCV viruria or isolated BKV viruria had renal dysfunction. Among the five patients with BKV in both urine and blood, two developed biopsy-proven BKV nephropathy associated with deterioration of the renal function. Management of the BKV nephropathy consisted of reduction of immunosuppression alone or in combination with antiviral treatment with cidofovir. This study shows that polyomavirus infection and related interstitial nephritis is a relevant clinical issue in the pediatric renal transplant population. Monitoring the polyomaviral load in the urine and the blood of the patients using a quantitative PCR technique is a useful tool in the diagnosis and subsequent management of this infection. Even before viremia is present, an important rise in the urinary viral load should draw the attention of the transplant clinician and raise the issue of adapting the immunosuppression.