[Characteristics of BK polymavirus infection in kidney transplant recipients]

To analyze the characteristics of BK polymavirus (BKV) infection and the optimal time window for intervention in kidney transplant recipients (KTRs).

We retrospectively analyzed the clinical data and treatment regimens in 226 KTRs in our center between January, 2013 and January, 2018. Among the recipients, 157 had a urine BKV load ≥1.0×10⁴ copy/mL after transplantation, and 69 had a urine BKV load below 1.0×10⁴ copy/mL (control group).

Among the 157 KTRs, 60 (38.2%) recipients were positive for urine BKV, 66 (42.0%) had BKV viruria, and 31(19.7%) had BKV viremia. The incidence of positive urine occult blood was significantly higher in BKV-positive recipients than in the control group (P < 0.05). The change of urine BKV load was linearly related to that of Tacrolimus trough blood level (r²=0.351, P < 0.05). In urine BKV positive group, the average estimated glomerular filtration rate (eGFR) was below the baseline level (60 mL·min^-1·1.73 m^-2) upon diagnosis of BKV infection reactivation, and recovered the normal level after intervention. In patients with BKV viruria and viremia, the average eGFR failed to return to the baseline level in spite of improvement of the renal function after intervention.

Positive urine occult blood after transplantation may be associated with BKV infection reactivation in some of the KTRs. BKV infection is sensitive to changes of plasma concentration of immunosuppressive agents. Early intervention of BKV replication in KTRs with appropriate dose reduction for immunosuppression can help to control virus replication and stabilize the allograft function.