Using Oral Vancomycin As Prophylaxis Against Clostridioides Difficile Infection in Stem Cell Transplant Recipients Is Associated with Increased Gram Negative Bacteremia

Background Infections complications continue to pose significant risk for patients undergoing hematopoietic stem cell transplantation (HSCT). Clostridioides difficile infection (CDI) has been identified as an independent risk factor for increased morbidity and mortality during HSCT with a reported incidence up to 9-fold higher compared with the general population. Patients are at high risk during protracted neutropenia and with concurrent risk factors such as antimicrobial exposure, mucosal damage from immunosuppressive chemotherapy/conditioning regimens, and transplant-specific factors such as graft versus host disease (GVHD).The data for safety and efficacy of a prophylactic strategy with oral vancomycin are limited. Our group previously reported decreased CDI rates in a small cohort with prophylaxis. Here we report an extended retrospective analysis from our institution with CDI rates, bacterial infectious complications, and transplant outcomes. Objectives Report outcomes for oral vancomycin as C. difficile prophylaxis during inpatient HSCT admission. Methods We performed retrospective chart review of consecutive patients who underwent HSCT at our program between 3/2021 to 5/2023. A total of 441 patients were divided into 2 cohorts: Group A (control) and Group B (patients who received oral vancomycin prophylaxis) during their HSCT inpatient hospital course. Prophylaxis consisted of vancomycin 125mg twice daily starting on the day of admission until discharge.The statistical analysis included descriptive elements, Chi-square and T-tests. Results Of 441 patients, 181 received vancomycin prophylaxis. Table 1 shows baseline characteristics. We identified 34 cases of CDI in the control group and 13 cases in group B (13 vs 7%; p=0.048). The overall positive blood culture rate was similar: 27% vs 33%. However, the incidence of gram-negative bacteremia incidence was 34 cases in group A and 41 cases in group B (13 vs 21.8%; p=0.008), shown in Figure 1 and Table 2 alongside additional engraftment and GVH data. Conclusion While OVP reduced the incidence of CDI, this was concurrently linked to a rise in the rate of gram-negative bacteremia, 21.8% vs 13%, in patients who underwent HSCT. GVHD outcomes were overall similar, although experienced earlier in the OVP group. We suspect this reflects altered gut microbiome secondary to OVP in patients who already have risk factors for bacterial translocation and are at risk for GVHD. A mortality signal emerged in patients undergoing autologous HSCT and treated with OVP that is not driven by CDI, bacterial infection, or GVH that warrants further investigation. Further studies are needed to identify the optimal subset of HSCT recipients for C. difficile prophylaxis but this strategy should be considered pragmatically given the increased rate of gram negative infections and potential mortality signal in our retrospective study.