Pre-engraftment bacteremia after allogeneic hematopoietic cell transplantation without primary fluoroquinolone antibacterial prophylaxis

Bacteremia is a common complication in allogeneic hematopoietic cell transplant recipients (alloHCTr), especially during the pre-engraftment period. International guidelines recommend antibacterial prophylaxis (ABP), despite potential selection for multidrug-resistant organisms (MDRO). Limited contemporary data exist on the epidemiology of pre-engraftment bacteremia in alloHCTr, who do not receive ABP. We performed a retrospective observational single-center cohort study including all consecutive adult alloHCTr (2015-2021), investigating the incidence, risk factors, and outcomes of bacteremia during the engraftment period. Primary fluoroquinolone (FQ) ABP is not routinely administered in our center. Among 421 patients identified, 124 bacteremia episodes were observed in 121/421 (29%) alloHCTr. The median time to the 1st bacteremia episode was 9 days (IQR 6-11). Most (105/124, 85%) episodes were monomicrobial, while >1 pathogens were identified in 19/124 (15%) episodes. Overall, 152 pathogens were isolated, with a predominance of Gram-positive (118/152, 78%), including coagulase-negative staphylococci (n:47), streptococci (n:46), and enterococci (n:15), followed by Gram-negative bacteria (GNB, 30/152, 20%), and anaerobes (4/152, 3%). There were 2/152 (1%) MDRO (extended-spectrum beta-lactamase producing) GNB. Multivariable analyses identified age >40-year-old (OR 2.4, P = 0.02), male gender (OR 1.8, P = 0.02), and a haploidentical/mismatched unrelated donor (OR 2.5, P < 0.001) as independent risk factors for bacteremia. All cause 30-day mortality among alloHCTr with bacteremia was 0.8% (1/121): one patient died due to an HCT-related complication. Despite lack of primary FQ ABP, low rates of bacteremia were observed during the pre-engraftment period, with low MDRO prevalence and mortality. Our findings may allow to revisit the need for primary universal FQ ABP in high-risk neutropenic hematology patients.