Analysis of BK Virus Infection in Children After Hematopoietic Cell Transplantation: A Retrospective Single-center Study

Background: BK virus (BKV) is one of the most common causes of hemorrhagic cystitis (HC) in children undergoing hematopoietic stem cell transplantation (HSCT). Viruses can be found in urine and serum of immunocompromised patients. Objective:This study aimed to evaluate the incidence, clinical course, and risk factors for BKV infection in children undergoing HSCT. Methods: Retrospectively analyzed children who underwent HSCT at Beijing Children's Hospital, Capital Medical University from June 2020 to June 2022. Data related to the clinical manifestations, engraftment, and prognosis were extracted from medical records. Patients were divided into the case group and the control group, according to the BKV infection or not after HSCT. Results: A total of 149 patients were enrolled in this study, and 61 (40.9%) patients developed BKV infection after HSCT. Among the 61 patients, BKV load was detected in all patients in urine samples and 22 patients in blood samples. The median value of BKV DNA copies in urine and plasma were 9.50x107 (5.37x102 to 6.84x109) copies/mL and 2.97x103 (9.96x102 to 3.58x108) copies/mL, respectively. The median time from beginning of the conditioning regimen to BKV infection was 23 (0 to 273) days, and the first positive time of urinary BKV was earlier than that of blood (13.5 d [0.0 to 123.0 d] vs. 30.5 d [7.0 to 165.0 d], P=0.003). Among the patients with BKV infection, 36 (59.0%) patients met the diagnosis of hemorrhagic cystitis (HC), and the incidence was higher than that in the control group (P<0.001). Similarly, 15 (24.6%) patients developed renal function damage in the case group and the proportion was higher than that in the control group. The median follow-up was 5.67 (0.03 to 24.90) months, and there was no significant difference in 1-year overall survival rate between the case group and the control group (84.2%+/- 5.7% vs. 95.3%+/- 2.3%, P=0.688), but the incidence of TA-TMA/VOD (31.1%) and diffuse alveolar hemorrhage (9.8%) in the case group was higher than that in the control group (P=0.002 and 0.038, respectively). Multivariate analysis showed that age above 5 years old (OR=9.039, 95% CI: 3.561-24.333, P<0.001) and use of MMF (OR=2.708, 95% CI: 1.041-7.044, P<0.05) were independent risk factors for BKV infection after HSCT. Conclusion: Among children after HSCT, the incidence of BKV infection was high and BKV infection was associated with an increased incidence of TA-TMA/VOD and diffuse alveolar hemorrhage. Patients older than 5 years of age at the time of HSCT and treated with MMF were more likely to develop BKV infection.