Retrospective study of antimicrobial prophylaxis and infections in patients with acute myeloid leukemia.

e18542 Background: In patients with acute myeloid leukemia (AML), infections are a major cause of morbidity and mortality. Fungal, bacterial, and viral prophylaxis are recommended during periods of neutropenia. However, evidence to support these recommendations is mixed, and uncertainty exists regarding optimal prophylactic therapy and duration. Methods: We performed a retrospective review of 63 patients with AML treated at Harbor-UCLA Medical Center from 2014 to 2024. Patients who received supportive care alone and those with acute promyelocytic leukemia were excluded. Results: Median age was 53 years old (range 19 – 84), and the cohort was 49% Hispanic, 21% Asian, 19% Black, 8% White, and 3% other. The most common induction therapies were 7 + 3 (63.5%), azacitidine (11.1%), azacitidine + venetoclax (6.3%), and 7 + 3 + midostaurin (4.8%). 55/63 (87.3%) patients received fungal prophylaxis, usually posaconazole (n = 47). 13/63 (20.6%) patients had a fungal infection (4 induction, 6 consolidation, 5 later line), and Aspergillus (n = 6) was the most frequent pathogen. 47/63 (74.6%) patients received viral prophylaxis with acyclovir or valacyclovir. 12/63 (19.0%) patients had a viral infection (7 induction, 1 consolidation, 5 later line). Viral infections included HSV (n = 5), coronavirus (n = 3), rhinovirus (n = 2), and VZV (n = 2). Bacterial prophylaxis, typically a fluoroquinolone, was used in 7/63 (11.1%) patients. Bacterial infections were observed in 49/63 (77.8%) patients, including 28 patients with more than 1 infection (45 induction, 30 consolidation, 44 later line). The most common infections were bacteremia (n = 55), UTI (n = 14), and pneumonia (n = 12). The risk of viral infection was significantly higher in patients without viral prophylaxis compared to patients who received prophylaxis (37.5% vs. 12.8%, p = 0.015). There were no significant differences in the rates of bacterial or fungal infection based on prophylaxis status. The rate of fungal infection was significantly higher in patients with adverse risk AML compared to patients with intermediate or favorable risk (41.2% vs. 13.0%, p = 0.0027). Six-month mortality from the time of fungal infection was 33.3%, compared to 23.9% for patients with no history of fungal infection (p = 0.253). At the time of last follow-up, 5/13 (38.5%) patients with a history of fungal infection were alive, compared to 24/50 (48%) patients without a fungal infection (p = 0.269). Infection was the cause in 23.5% of patient deaths. Conclusions: In this single-center retrospective study, fungal and viral prophylaxis were used in most patients, whereas bacterial prophylaxis was rare. Bacterial infections were frequently encountered with a high rate of bacteremia. Aspergillus was the most common fungal pathogen, reinforcing the importance of mold-active fungal prophylaxis. HSV was the most common viral pathogen, and prophylaxis reduced the risk of infection.