Legionella Micdadei Pneumonia Mimicking Miliary Tuberculosis in an Elderly Traveller: A Diagnostic Challenge

Legionella micdadei is an uncommon cause of atypical pneumonia and may be underrecognized because routine diagnostic testing primarily identifies Legionella pneumophila. Clinical and radiologic manifestations are variable and, in rare instances, may mimic miliary tuberculosis, creating significant diagnostic uncertainty and potential delays in appropriate therapy.

A 77-year-old male presented with persistent headache, fatigue, decreased appetite, and unintentional weight loss following several weeks of flu-like symptoms after recent travel to Pakistan. Imaging demonstrated innumerable diffuse pulmonary micronodules concerning for miliary tuberculosis. The patient was placed in airborne isolation and empirically treated with anti-tuberculous therapy. Extensive microbiologic testing, including sputum studies and serologic evaluation, was negative. Because sputum samples could not be obtained, bronchoscopy with bronchoalveolar lavage (BAL) was performed. Molecular testing of BAL fluid identified L. micdadei. Anti-tuberculous therapy was discontinued and treatment with levofloxacin was initiated, resulting in rapid clinical improvement.

This case highlights a rare presentation of L. micdadei pneumonia with diffuse pulmonary micronodules mimicking miliary tuberculosis. Recognition of this atypical presentation and the use of advanced diagnostic techniques such as bronchoscopy and molecular testing are essential for establishing the correct diagnosis and guiding appropriate management.

Legionella micdadei pneumonia can rarely present with diffuse pulmonary micronodules mimicking miliary tuberculosis, leading to potential diagnostic misinterpretation.Standard urinary Legionella antigen testing primarily detects L. pneumophila; therefore, molecular diagnostics such as bronchoalveolar lavage polymerase chain reaction may be required to identify non-pneumophila species.