Mycobacterium kansasii is a nontuberculous, slowly growing mycobacterium. Nontuberculous mycobacteria are frequently isolated from the environment, and M. kansasii can be isolated from tap water.

Mycobacterium kansasii is the second most common cause of nontuberculous mycobacterial disease in the United States. It primarily affects middle-aged men of Northern European descent but can affect patients of any age, sex, or race. Infection with this organism can result in a variety of clinical syndromes. A single positive sputum culture with M. kansasii is not proof of infection and needs to be considered as part of the patient's overall clinical presentation as colonization, particularly in the setting of structural lung disease, is not well documented.

Pulmonary evolvement mimics that of patients with Mycobacterium tuberculosis. Patients can present with cavitary lung disease and upper lobe predominance. They have chronic cough that may or may not be productive. They may have fever, hemoptysis, and weight loss.

Mycobacterium kansasii infection can also present with a chronic nodular lung disease with similar manifestations to infection with Mycobacterium avium complex or Mycobacterium abscessus.

Skeletal infection (involving bone, joints, or tendons) can also be seen. Less frequently, infection with this pathogen may cause cervical (or other) lymphadenitis or skin and soft tissue disease.

Infection with the human immunodeficiency virus (HIV) is a risk factor for M. kansasii infection, although patients without HIV can also be affected.