Risk factors and clinical outcomes of infectious events in the first 24 months after kidney transplant in a large retrospective cohort

OBJECTIVES: Kidney transplant recipients remain highly vulnerable to infectious complications, particularly in the early post-transplant period, with potential effects on hospitalization, graft outcomes, and survival. We aimed to quantify the incidence, timing, microbiology, predictors, and clinical impact of infections occurring within 24 months after kidney transplantation in a large contemporary single-center cohort. METHODS: We retrospectively analyzed 784 adult kidney transplant recipients transplanted between 2013 and 2023 at Padua University Hospital. Infectious events were defined using microbiological documentation and standardized clinical criteria; cumulative incidence was modeled with Fine-Gray competing risk regression (graft loss and death as competing events). Predictors of 2-year mortality were explored using Cox regression. RESULTS: Overall, 486 recipients (62.0%) experienced at least one infectious event, and 253 (32.3%) had multiple episodes. Bacterial infections were most frequent (43.2%), dominated by urinary tract infections (33.2% overall), followed by viral infections (28.6%; mainly cytomegalovirus reactivation 16.5% and BK polyomavirus 8.8%) and fungal infections (3.2%), largely because of Candida spp. Median time to first infection was early (approximately 2 months), and infections were associated with substantial hospitalization burden. In multivariable competing risk models, female sex (sub-distribution hazard ratio sHR 1.50, 95% confidence interval CI 1.25-1.80), multimorbidity (sHR = 1.25, 95% CI 1.01-1.55) and mycophenolate immunosuppressive combination (sHR 1.41, 95% CI 1.10-1.80) independently predicted any infection. Living-donor transplantation was independently associated with viral infections (sHR 1.42, P = 0.034). Two-year mortality was low (2.9%) and was mainly associated with infection (HR: 4.17, 95% CI: 1.23-14.29; P = 0.021). CONCLUSION: Infections remain highly prevalent within 24 months after kidney transplantation; risk-adapted prevention and tailored immunosuppression strategies should prioritize recipients at increased risk, particularly women, combined-transplant recipients, and those with high comorbidity burden.