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Mycobacterium avium complex is ubiquitous in the environment and is the most frequent cause of pulmonary infection due to nontuberculous mycobacteria in the United States. Patients with isolated pulmonary M. avium complex are typically immunocompetent adults, most commonly with underlying lung disease, or postmenopausal women who present with a chronic cough and have nodular opacities with bronchiectasis in the right middle lobe on chest imaging (Lady Windermere syndrome). Sputum cultures show acid-fast bacilli.

Gram-positive diplococci would be seen with Streptococcus pneumoniae infection, which manifests with acute pulmonary symptoms and lobar consolidation.

Histoplamosis is caused by a budding yeast, but bronchiectasis is not a typical risk factor for histoplasmosis.

Small, pleomorphic gram-positive rods include organisms such as Rhodococcus, Listeria, Corynebacterium, and Propionibacterium. Although Rhodococcus can cause respiratory infection, immunocompromised hosts are particularly prone to this type of pneumonia.

Candida is a yeast that may form pseudohyphae, but this organism is an uncommon cause of respiratory infection.

Last reviewed Jan 2018. Last modified Dec 2015.

Citations

Ebihara T and Sasaki H. Image in clinical medicine. Bronchiectasis with Mycobacterium avium complex infection. N Engl J Med 2002 May 3; 346:1372. > View Abstract

Kasperbauer SH and Daley CL. Diagnosis and treatment of infections due to Mycobacterium avium complex. Semin Respir Crit Care Med 2008 Sep 24; 29:569.   > View Abstract