Evaluation of the Bacterial Etiologies of Infections in Patients Undergoing Hematopoietic Stem Cell Transplantation

Objectives: Bacterial infections increase morbidity and mortality in patients undergoing hematopoietic stem cell transplantation (HSCT). The characteristics of the bacteria causing infections in these patients undergo dynamic changes both globally and locally during the transplantation process. The etiology of bacterial isolates and analysis of changes in the antibiotic sensitivities are crucial for the selection of appropriate prophylactic and empiric therapies. In this study we aimed to evaluate the first episode of bacterial infection in patients undergoing allogeneic or autologous hematopoietic stem cell transplantation and to identify bacterial isolates and the resistance profile of causative bacteria.

Materials and Methods: In this retrospective study, the charts of 195 patients who underwent allogeneic or autologous hematopoietic stem cell transplantation between January 2010 and December 2013 were reviewed. Ninety-six patients who had microbiologic evidence of bacterial infection were included in the study. The culture results from the first infectious episode during the transplantation process were evaluated. Patients were grouped according to the type of transplantation, and categorized according to the transplantation process, presence of neutropenia and infection status. Microbiological examination of samples obtained for culture and sensitivity analysis were performed according to standards of the National Committee for Clinical Laboratory Standards Institute (CLSI).

Results: Gram-negative and Gram-positive bacteria were identified in 54.2% and 44.8% of the infectious episodes, respectively. Poly-microbial etiology was identified in only 1.0% of these episodes. E. coli and coagulase-negative staphylococci (CoNS) were the most frequently isolated pathogens. In the early stage infections, Gram-positive organisms were more frequently isolated (72.1%) (p=0.042) and a significantly larger number of patients had undergone autologous stem cell transplantation (p<0.001). This situation was explained by the absence of antimicrobial prophylaxis in the autologous group, intensive induction chemotherapy, presence of catheter and mucosal damage. The frequency of extended-spectrum β-lactamase (ESBL) was found to be very high in the allogeneic group compared to the autologous group (36.4% vs. 13.3%). All of the staphylococcal isolates in the allogeneic group were noted to be methicillin resistant.

Conclusions: Treatment and prophylaxis have become increasingly more challenging with the infections caused by resistant pathogens. It is imperative to carefully monitor causative agents of bacterial infections and to plan prophylactic and empiric treatments according to characteristics of the individual patients.