Aims: Cytomegalovirus (CMV) infection is a common complication post pediatric kidney transplant (KT). Valganciclovir (VCG) is indicated for prophylaxis and treatment. This study aims to define CMV infection epidemiology during the first year post-KT and to evaluate the influence of VCG on kidney function.
Methods: We conducted a retrospective study including pediatric patients (<21 years) who received KT between January 2014 - February 2024, with a ≥ 12 months follow-up.
The immunosuppression protocol consisted of Basiliximab or Thymoglobuline for induction, followed by Calcineurin inhibitors, Mycophenolate mofetil, Azathioprine or Everolimus, and Prednisone for maintenance.
Patients were risk-stratified based on pre-transplant CMV serostatus: high-risk (donor+/recipient-), medium-high risk (donor+/recipient+), medium-low risk (donor-/recipient+) and low-risk (donor-/recipient-).
A 3-month VCG-prophylaxis was administered to the high-risk group and to those who received ATG induction. CMV-DNAemia was defined by a CMV polymerase chain reaction test result >250 copies/mL in blood. VCG pre-emptive treatment was initiated if CMV DNAemia exceeded 500 copies/mL. Follow-up data were collected at baseline and months 3-6-9-12 after KT.
Results: Of the 137 transplanted patients, 104 met the inclusion criteria, while 33 were excluded due to loss to follow-up (27), death (2), acute rejection (1), primary disease relapse (1), renal vein thrombosis (1) and infection (1).
Table 1 summarizes features of our cohort.
VCG prophylaxis was administered to 32/104 patients (31%) with a median dose of 17 mg/kg/die (IQR:10.4-19.7). CMV DNAemia was detected in 38/104 (36.5%) overall patients: 47% in high-risk, 27% in medium-high risk, 13% in medium-low risk, and 13% in low-risk group respectively. The incidence was significantly different between risk groups (p=0.03). Splitting the groups by age we noted that the difference between risk groups was more evident in the scholar-age patient group. In high-risk group, infection occurred at a median time of 53 days (IQR:26.5-64.5) after prophylaxis ended, with a median infection duration of 40 days (IQR:21.3-49.7), longer but not statistically significant compared to other groups. Within the medium-risk group, donor+/recipient+ showed higher infection rates compared to donor-/recipient+ (p=0.37), however not statistically significant. 
VCG treatment was administered with a median dose of 30 mg/kg/die (IQR 21.2-39.1). No major adverse events were noted. VCG-treated and non-VCG-treated patients had similar median ΔGFR (3-12 month): 8.55 vs. 8.6 mL/min/1.73 m² respectively.
Conclusions: Paediatric KT recipients are at high risk for CMV-DNAemia despite VCG prophylaxis, which does not affect renal function. Given the early post-prophylaxis infection onset in the high-risk group, extended prophylaxis may be beneficial. Moreover, prophylaxis may be also indicated for the medium-high risk group, particularly for younger patients.