Case Series Highlights Bacillus Cereus Risk in Patients With AML, Neutropenia

Bacillus cereus can lead to serious invasive infections, neurological complications, and even death in immunocompromised patients. A new case series highlights the risk for patients with acute myeloid leukemia (AML) and persistent neutropenic fever and explains one strategy to reduce the potential harm.

The report was published in Open Forum Infectious Diseases.

B cereus—a gram-positive, rod-shaped bacterium—is ubiquitous, noted the study authors from at Brigham and Woman’s Hospital in Boston. For patients with AML or neutropenia, the bacterium can cause sepsis and neuroinvasive disease, leading to complications that include meningoencephalitis, brain abscess, and cerebral hemorrhage. Even with timely antimicrobial therapy, neuroinvasive B cereus is often fatal, the authors added.

Magnified image of Bacillus cereus

Image Credit: DrMicrobe - stock.adobe.com

Due to B cereus’ β-lactamase production, infection from the bacterium cannot be treated with β-lactam therapy, they noted.

“Recommended therapies are vancomycin, carbapenems, or fluoroquinolones, although isolates resistant to each of these antimicrobial classes have been reported,” Little and colleagues noted.

One challenge with B cereus is that it can be difficult to trace cases back to a single point of origin. For instance, the report’s authors said they experienced a cluster of neuroinvasive B cereus infections in 2013 and 2014. Although they could not identify a clear source, “there was evidence linking cases to Bacillus contamination of unpeeled banana associated with nearby construction. In response to the cluster, their health system stepped up their cleaning practices and temporarily changed their protocols for fever and neutropenia, including adding empiric ciprofloxacin therapy for patients with AML who were receiving induction chemotherapy and had persistent or recurrent neutropenic fever.

“Following the discontinuation of these measures, 3 patients with AML developed health care–associated neuroinvasive B cereus infections in close temporal proximity in 2022, triggering an extensive epidemiologic investigation that identified 2 additional cases between 2018 and 2022,” the authors said.

The new report describes their experience with those cases. The new case series had similar characteristics to the 2013-2014 cluster. In each case between 2018 and 2022, the patient was undergoing induction chemotherapy and had neutropenia, and all experienced neurological symptoms, although the investigators said they did not have microbiologic confirmation of B cereus in the central nervous system (CNS). They added, however, that the timing of the CNS complications—occurring a median of 1 day after diagnosis—was “highly suggestive of neuroinvasive disease.”

All 5 patients survived after treatment with ciprofloxacin “with limited or no neurologic sequelae.”

The authors said they were unable to pinpoint a point source for the cases. Like in the earlier cluster, they added ciprofloxacin to their empiric antimicrobial regimen for patients with similar characteristics, and as of 1 year after the change, there had been no new cases.

The authors said early identification of B cereus is important but can be difficult in patients with profound neutropenia or thrombocytopenia.

“In fact, the clinical association of neurologic events with invasive B cereus infection has primarily been described through postmortem studies,” they wrote. “For patients who survive, B cereus is often identified only on blood culture, as was the case in this series.”

Therefore, they said, clinicians treating immunocompromised patients with B cereus bloodstream infections should be vigilant about the potential for neurologic complications.

“These infections may be underrecognized, and even though they have been associated with nosocomial outbreaks, due to the ubiquity of B cereus, they can also occur as sporadic infections associated with independent environmental or dietary exposures,” they wrote.

The investigators concluded that physicians may reduce the risk of morbidity by deploying antimicrobials, but they added that they should limit such use to high-risk patients given the broader concerns about antimicrobial resistance.

Reference

Little JS, Coughlin C, Hsieh C, et al. Neuroinvasive Bacillus cereus infection in immunocompromised hosts: epidemiologic investigation of 5 patients with acute myeloid leukemia. Open Forum Infect Dis. 2024;11(3):ofae048. doi:10.1093/ofid/ofae048