Likelihood of Bacterial Infection in Immunocompromised Patients Treated With IV Antibiotics

Introduction: Clinicians have low thresholds to give immunocompromised hosts (ICH) with possible sepsis immediate, broad-spectrum antibiotics given their high risk for poor sepsis outcomes. Clinical presentations in ICH, however, are protean and non-bacterial infections and non-infectious conditions are common. We assessed the frequency of bacterial infection in retrospect among ICH vs non-ICH patients treated for possible sepsis in the emergency department.


Methods: We retrospectively reviewed the medical records of 350 adults treated for possible sepsis in 9 Mass General Brigham affiliated emergency departments between 2022-2024, defined as blood cultures drawn, lactate drawn, and intravenous antibiotics administered within 6h of arrival. Cases were oversampled based on ICH status, assigned using administrative codes and manually confirmed with CDC criteria. We used a structured framework to determine the post-hoc likelihood of bacterial infection (definite, probable, possible, or highly unlikely).


Results: Of the 350 patients, 186 (53.1%) were ICH and 164 (46.9%) non-ICH per CDC criteria. ICH were more likely to present with fevers, chills or rigors (66% vs 32%, p < 0.001) whereas non-ICH more often endorsed no infectious symptoms (21% vs 40%, p< 0.001). ED providers documented concern for sepsis in more ICH vs non-ICH (74% vs 62%, p=0.01). Despite this, post-hoc likelihood of bacterial infection was similar in ICH vs non-ICH (definite or probable: 46.2% vs 48.8%, p=0.48; possible or highly unlikely: 53.8% vs 51.2%, p=0.63). In ICH without definite or probable bacterial infection, common etiologies for presentation included febrile neutropenia (37%), viral or fungal infection (35%), chronic lung disease exacerbations (17%), progression of malignancy (9%), chemotherapy toxicity (7%), aspiration pneumonitis (6%), and chronic heart disease exacerbations (6%).


Conclusions: Fewer than half of ICH treated for possible sepsis in the ED had definite or probable bacterial infection in retrospect, a rate similar to non-ICH despite more ICH frequently presenting with infectious symptoms and triggering concern for sepsis. These findings underscore the diagnostic complexity of sepsis evaluation in ICH and highlight the array of conditions that can mimic sepsis in this population.