Morganella Morganii Respiratory Infection as an Initial Presentation of Acute Myeloid Leukemia With Monocytic Differentiation: A Rare Opportunistic Pathogen in a Newly Diagnosed Immunocompromised Host.

Infective manifestations of hematological malignancies can be traced to a variety of pathogens, necessitating broad spectrum empiric antibiotic coverage, and prompt identification of pathogenic microbes to improve clinical outcomes. We present a case of Morganella morganii leading to pneumonia as the presenting illness in a previously undiagnosed, functionally neutropenic adult presenting with acute myeloid leukemia with monocytic differentiation. Our patient was a 64 year old man with no prior medical care who presented with complaints of progressive abdominal pain, productive cough and fevers. Chest radiography revealed no organized consolidations, and computed tomographic imaging of the chest showed bibasilar atelectasis and trace pleural effusions. Laboratory analysis revealed marked leukocytosis with predominant monocytosis, and circulating blasts, suggestive of acute myeloid leukemia with monocytic differentiation, later confirmed with bone marrow biopsy. The patient was initially started on guideline directed empiric therapy for respiratory infection, with sputum cultures later found to be growing Morganella morganii, necessitating a change in antimicrobial therapy, following which the patient showed clinical improvement. To our knowledge, this is the first reported case of Morganella morganii pneumonia presenting at the initial diagnostic encounter of de novo acute myelomonocytic leukemia. This report underscores the need for prompt microbiologic evaluation, broad empiric coverage with early de-escalation, and inclusion of M. morganii in the differential diagnosis of pneumonia in functionally neutropenic patients when standard pathogens are not identified. This case highlights the need to recognize atypical Gram-negative organisms as potential pathogens in these populations, even in the absence of characteristic radiographic findings.