At least 30 acid-fast bacilli other than those causing tuberculosis and leprosy have been identified. These are known as atypical mycobacteria (ATM). About a dozen of these may cause cutaneous disease; they are found worldwide in water, moist soil, house dust, dairy products, cold-blooded animals, vegetation, and human feces.

The most common of those causing disease in humans (usually the immunocompromised) are Mycobacterium marinum, Mycobacterium haemophilum, Mycobacterium kansasii, and the rapidly growing members of the Mycobacterium fortuitum complex (M. fortuitum, Mycobacterium chelonae / abscessus group and Mycobacterium smegmatis). Disease with Mycobacterium avium intracellulare is described separately. Mycobacterium ulcerans is a common disease in tropical areas, but does not seem to increase in incidence with immunosuppression. A few other ATM species are sometimes reported in human immunodeficiency virus (HIV)-infected patients but rarely cause disease in the immunocompetent host.

Infection is acquired by inhalation, ingestion, or percutaneous penetration (including tattoos). Clinical presentation of disease depends upon the species, method of acquisition, and the host immune state.

Infection presents as pulmonary disease, lymphadenitis, skin and soft tissue infection (the most common presentation in the immunocompetent), or disseminated disease.

Infection with these organisms is being increasingly recognized, particularly in HIV-infected patients with disseminated disease. The immunocompromised and the elderly are more at risk. Underlying factors include HIV, autoimmune disease, renal or cardiac transplantation, preceding lung disease, and chemotherapy.

Cutaneous lesions may be painful, as is joint involvement. Patients with pulmonary disease may have a chronic cough and hemoptysis. Those with disseminated disease may present with fatigue, night sweats, and weight loss. Signs of disease include lymphadenopathy, fever, rales, rhonchi, joint edema and erythema, heart murmur, and keratitis or corneal ulceration.

Mycobacterium marinum (fish-tank or swimming pool granuloma)
The organism occurs worldwide in fresh and saltwater. It is probably pathogenic in only abraded skin. Occupational or recreational water exposure occurs in the majority of cases. Skin lesions appear 2-3 weeks after inoculation (but may occur months later). Lymph nodes may be enlarged, and lesions may be multiple in a sporotrichoid pattern. Tenosynovitis, osteomyelitis, and septic arthritis may occur. Dissemination may occur in the immunocompromised. In the immunocompetent, lesions may spontaneously resolve. Disease is usually successfully treated.

Mycobacterium kansasii
The organism is ubiquitous but more commonly reported from temperate zones (particularly the United States, United Kingdom, northern France, and Belgium). It usually causes pulmonary disease in middle-aged men with preceding pulmonary disease. It rarely causes cutaneous disease, but the majority of these cases are in the immunocompromised (chemotherapy, autoimmune disease, AIDS, or solid organ transplantation). Skin lesions may be localized or disseminated. After M. avium intracellulare, M. kansasii is the most frequent cause of disseminated mycobacteriosis in AIDS-infected patients.

Mycobacterium fortuitum complex, M. chelonae / abscessus, and M. smegmatis
These rapidly growing mycobacteria cause skin, soft tissue, bone, and pulmonary infection. They are widely distributed in soil and water as well as sometimes being commensals on the skin surface. Infection has also been associated with the use of contaminated whirlpool footbaths during pedicures at nail salons. Infection of the immunocompetent host is usually confined to local cutaneous abscess formation. Immunocompromised patients often lack a history of trauma and may present with disseminated disease with skin lesions, cervical lymphadenitis, keratitis, osteomyelitis, and endocarditis.

Mycobacterium haemophilum
This organism found in soil and water may cause skin, joint, or less often, pulmonary disease in the immunocompromised (particularly with HIV infection, transplants, hematologic malignancy, and after immunosuppressive therapy). Lesions are often multiple, tender, and may be accompanied by weight loss, tenosynovitis, osteomyelitis, or pulmonary symptoms.