Impact of Cytomegalovirus Infection on Transplant Outcomes after Allogeneic Hematopoietic Stem Cell Transplantation: A Retrospective Single-Center Study

Background and Objectives CMV infection remains a common and clinically significant complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT), particularly in the setting of profound post-transplant immunosuppression. CMV reactivation occurs frequently in the early post-transplant period and represents a major challenge in clinical management, especially among seropositive recipients. It may contribute not only to direct organ involvement but also to indirect effects, including increased susceptibility to secondary infections and impaired immune reconstitution. The clinical impact of CMV reactivation may vary depending on patient-related and transplantrelated factors, reflecting the heterogeneity of the transplanted population. Despite advances in viral monitoring and preemptive therapy, CMV reactivation continues to be associated with an increased risk of post-transplant complications and higher mortality rates. This study aimed to assess the frequency of CMV reactivation and evaluate its impact on complications and early post-transplant mortality in a retrospective single-center cohort. Material and Method A retrospective single-center study was conducted including 77 patients who underwent allogeneic hematopoietic stem cell transplantation at the Hospital of Lithuanian University of Health Sciences Kaunas Clinics between 2020 and 2025. The study population consisted of adult patients with a median age of 56 years, with a balanced sex distribution, and predominantly myeloid underlying diseases. CMV reactivation was monitored using quantitative polymerase chain reaction. Associations between CMV reactivation and post-transplant complications as well as early posttransplant mortality were analyzed using appropriate statistical methods, including chisquare or Fisher’s exact test for categorical variables and non-parametric tests for continuous variables. Early mortality was defined as death during the initial posttransplant hospitalization or within 100 days after transplantation, whichever occurred later. Multivariate logistic regression analysis was performed to identify independent risk factors. IBM SPSS Statistics (version 30.0.0) was used for statistical analysis. A p-value < 0.05 was considered statistically significant. Results CMV reactivation was observed in 53.2% of patients and occurred in 58.0% of seropositive recipients with available serostatus data. The median time to CMV reactivation was 14 days after transplantation (IQR 7.5–27.5), with a mean of 17.8 ± 12.0 days. Antiviral treatment for CMV infection was required in 43.9% of patients with reactivation, reflecting a substantial clinical burden of CMV management after transplantation. CMV reactivation was more frequently observed in patients who developed graft-versus-host disease (65.0% vs. 49.1%), although this difference did not reach statistical significance. Patients with CMV reactivation had a higher frequency of infectious complications (70.7% vs. 55.6%) and overall complications (85.4% vs. 72.2%) compared to those without reactivation; however, these associations did not reach statistical significance. A similar trend was observed across different complication types, suggesting a consistent pattern despite the lack of statistical significance. No significant association was found between CMV DNA load and the number of complications; however, this finding should be interpreted with caution given the limited sample size. CMV reactivation was associated with significantly increased early post-transplant mortality (36.6% vs. 11.1%; p = 0.010), indicating a clinically meaningful impact on early outcomes. In multivariate analysis adjusted for age and graft-versus-host disease, CMV reactivation remained an independent predictor of early mortality (OR = 5.00; 95% CI: 1.44–17.39; p = 0.011). These findings highlight the clinical relevance of CMV reactivation in the early post-transplant period. Conclusions and Recommendations CMV reactivation is a frequent complication after allo-HSCT and was associated with significantly increased early post-transplant mortality, remaining an independent predictor after adjustment for relevant clinical factors. A consistent trend towards higher rates of infectious and overall complications was observed in patients with CMV reactivation, although statistical significance was not reached. In contrast to findings reported in the literature, no association was identified between CMV DNA load and complication burden, which is likely related to the limited sample size of this study. The relatively small cohort (n = 77) may have reduced the statistical power to detect significant associations. These findings highlight the importance of careful CMV monitoring and timely antiviral intervention in the early post-transplant period. Further studies with larger cohorts are needed to better define the clinical impact of CMV reactivation and to validate these findings.