The Republican Center for Hematology and Bone Marrow Transplantation is a national clinical and research center for adult patients located in Minsk, Republic of Belarus. The clinical departments are based in the 9th Clinical Hospital of Minsk, which is one of the largest teaching hospitals in Belarus, performing more than 100 HSCTs annually. The Center has 150 beds, including an intensive care unit, for patients with various hematological diseases and patients undergoing HSCT. The Center also includes laboratories for microbiology, bone marrow separation and freezing, cellular biotechnology, human leukocyte antigen (HLA)-typing, and clinical diagnostics.

A prospective observational study was performed to determine the possible risk factors for adverse outcome in adult patients with microbiologically proven BSI in the pre-engraftment period after HSCT. The indications for HSCT included acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, myelodysplastic syndromes, multiple myeloma, Hodgkin's lymphoma, and non-Hodgkin's lymphoma. The study was approved by the Scientific and Ethical Committees of the Republican Center for Hematology and Bone Marrow Transplantation in Minsk, Republic of Belarus.

The primary outcome in this study was all-cause 30-day mortality after onset of febrile neutropenia. The covariates included in analysis were: patient age and gender characteristics, type of HSCT (autologous/allogeneic), conditioning chemotherapy regimen (myeloablative/non-myeloablative or reduced intensity), primary diagnosis, level of neutropenia on the day that the first positive blood culture was collected, isolation of carbapenem-resistant non-fermenting gram-negative bacteria (Acinetobacter baumannii and Pseudomonas aeruginosa), isolation of extended-spectrum beta-lactamases (ESBL)-producing member of Enterobacteriaceae spp. family, isolation of methicillin-resistant S. aureus (MRSA), and adequacy of empirical antibacterial therapy.

Epidemiological, clinical, and laboratory data were prospectively collected for patients aged 18–70 years undergoing HSCT from January 2013 to October 2015. The exclusion criteria included concurrent active oncological disease, hepatitis B or hepatitis C infection, active fungal disease, rheumatological diseases, and diabetes mellitus. Patients with possible active cytomegalovirus (CMV) infection (monitored using real-time quantitative polymerase chain reaction) were also excluded from the study. All patients had a complete clinical and hematological remission of the main disease at the start of HSCT. Blood cultures were obtained from all patients with standard precautions and fulfilled the criteria of febrile neutropenia in the pre-engraftment period after HSCT, with identification and in vitro antibiotic susceptibility testing. Every patient with BSI was followed for at least 30 days after collection of the first positive blood culture. Only first bacteremia episodes were included in the analyses.

Empirical antimicrobial therapy was defined as adequate if it was administered <24 hours after collection of blood cultures and if the microorganisms subsequently isolated in vitro were susceptible to at least one of the administered antibiotics. Empirical antimicrobial therapy was defined as inadequate if the subsequently isolated microorganisms were resistant or intermediately susceptible in vitro to all of the administered antibiotics, or the empiric antibacterial therapy was administered >24 hours after collection of blood cultures or the dosing regimen conflicted with the standard dosing recommendations. The 30-day mortality was defined as the number of patients with BSI who died within 30 days after the onset of febrile neutropenia divided by the total number of patients with BSI. Adverse outcome was defined as death within 30 days from the onset of febrile neutropenia. The pre-engraftment period after HSCT was defined as the period from day 0 to day 30 after HSCT [7]. BSI was defined as having a microbiologically proven growth from a blood culture after HSCT in patients with febrile neutropenia. The criteria for febrile neutropenia included a single oral temperature measurement >38.3℃ or a temperature >38.0℃ sustained over a 1-h period in a patient with absolute neutrophil count (ANC) of <500 cells/µL or an ANC expected to decrease to <500 cells/µL during the next 48 hours [8].

Transplantations were performed according to institutional protocols. Briefly, the most frequent myeloablative conditioning regimens were busulfan plus cyclophosphamide or cyclophosphamide plus total-body irradiation. Non-myeloablative and reduced-intensity conditioning mainly included fludarabine with melphalan or treosulfan and BEAM regimen (carmustine, etoposide, cytarabine, melphalan). Graft-versus-host disease (GVHD) prophylaxis regimens included cyclosporine, methotrexate, and tacrolimus. Antithymocyte globulin was administered in cases of unrelated donors. Standard antibacterial prophylaxis in the department was based on fluoroquinolones (mainly ciprofloxacin 0.5 g BID orally) starting from the initiation of the conditioning regimen until the level of neutrophils in the peripheral blood exceeded 500 cells/µL. No routine antibacterial prophylaxis against Streptococcus pneumoniae was administered. Antifungal prophylaxis with fluconazole was prescribed to patients undergoing autologous HSCT, while micafungin was used as antifungal prophylaxis in patients undergoing allogeneic HSCT. Prophylaxis against Pneumocystis jirovecii with trimethoprim-sulfamethoxazole was administered to all patients until immunologic recovery after HSCT. Acyclovir was used as prophylaxis for infections caused by herpes viruses. Real-time quantitative polymerase chain reaction was used to monitor CMV DNA levels in HSCT patients weekly during the pre-engraftment period with ganciclovir as the first-line pre-emptive therapy in case of possible active CMV infection and exclusion of such patients from the study. During the period of severe neutropenia (ANC <100 cells/µL), all patients were isolated in single rooms with positive pressure, laminar air flow, and high-efficiency particulate air filtration. After the ANC exceeded 100 cells/µL, some of the clinically stable patients were moved to the intensive care department with two patients per room and positive air pressure.

The institution's standard protocols for initial empirical antibiotic therapy for treatment of febrile neutropenia included cephalosporins (cefepime or cefoperazone/sulbactam) or carbapenems (imipenem/cilastatin or meropenem) depending on the patient risk group, with an addition of vancomycin in cases of possible infection caused by gram-positive pathogens [9].

In every patient with febrile neutropenia before administration of antibacterial therapy, 10 mL of blood was taken both from the peripheral vein and the central venous catheter with standard aseptic precautions and cultivated in aerobic/anaerobic bioMerieux BacT/ALERT culture media in a BacT/ALERT 3D automated microbial detection system until receiving positive results or until the seventh day. In cases of positive results, the microbial culture was isolated and grown on different manufactured culture media. Identification and antimicrobial susceptibility testing were performed using a bioMerieux VITEK 2 automatic system, and the ESBL phenotype was determined using a VITEK 2 ESBL Test System. Additional antimicrobial susceptibility in carbapenem-resistant strains (resistance to imipenem, meropenem, and doripenem) was confirmed by E-tests and disc-diffusion assays. The minimum inhibitory concentration (MIC) breakpoints used for susceptibility testing were most current Clinical and Laboratory Standards Institute (CLSI) guideline at the start of the study [10]. The criteria for establishing a bacterial isolate as clinical significant included clinical signs of active infection or isolation of the same microorganism with identical antimicrobial resistance profiles from more than one blood culture bottle or more than once during a one-week period.

Non-parametric statistics for categorical (Chi-squared or Fisher's exact tests) and quantitative (Mann-Whitney U-test, Odds Ratio) variables were used for statistical analysis. The distributions of the variables were determined using the Shapiro-Wilk test. Multivariate analysis was performed using logistic regression methods for categorical variables with P≤0.2 in univariate analysis. Data processing and analysis was performed using MedCalc Statistical Software v.14.10.2 (MedCalc Software bvba, Ostend, Belgium), and results were considered statistically significant for P<0.05.