Nontuberculous Mycobacteria Infections

Key Features

Essentials of Diagnosis

• Chronic unilateral cervical lymphadenitis

• Granulomas of the skin

• Chronic bone lesion with draining sinus (chronic osteomyelitis)

• Tuberculin skin test (TST) of 5–8 mm, negative chest radiograph, and negative history of contact with tuberculosis

• Diagnosis by positive culture

• Disseminated infection in patients with AIDS

General Considerations

• More than 130 species of acid-fast mycobacteria other than M tuberculosis may cause subclinical infections and occasionally clinical disease resembling tuberculosis

• Strains of nontuberculous mycobacteria (NTM) are common in soil, food, and water

• Organisms enter the host by small abrasions in skin, oral mucosa, or gastrointestinal mucosa

• Mycobacterium avium complex (MAC), Mycobacterium kansasii, Mycobacterium fortuitum, Mycobacterium abscessus, Mycobacterium marinum, and Mycobacterium chelonae are most commonly encountered

• M fortuitum, M abscessus, and M chelonae are "rapid growers" requiring 3–7 days for recovery, whereas other mycobacteria require several weeks

• After inoculation, they form colonies closely resembling M tuberculosis morphologically

Clinical Findings

• Lymphadenitis

  • MAC is the most common organism

  • A submandibular or cervical node swells slowly and is firm and initially somewhat tender

  • Low-grade fever may occur

  • Over time, the node may suppurate and drain chronically

  • Nodes in other areas of the head and neck and elsewhere are sometimes involved

  • Chronic intermittent drainage is common, but in many cases healing occurs after 4–12 months

• Pulmonary disease

  • In the western United States, usually due to M kansasii or MAC

  • In the eastern United States and in other countries, usually caused by MAC

  • Presentation is clinically indistinguishable from that of tuberculosis

  • Adolescents with cystic fibrosis may be infected with nontuberculous mycobacteria with resulting fever and declining pulmonary function

• Swimming pool granuloma

  • Commonly due to M marinum

  • A solitary chronic granulomatous lesion with satellite lesions develops after minor trauma in infected swimming pools or other aquatic sources

  • Minor trauma during exposure to home aquariums or other aquatic environments may also lead to infection

• Chronic osteomyelitis

  • Caused by MAC, M kansasii, M fortuitum, or other rapid growers

  • Swelling and pain over a distal extremity, radiolucent defects in bone, fever, and clinical and radiographic evidence of bronchopneumonia are present

  • Cases are rare

• Meningitis

  • Caused by M kansasii

  • May be indistinguishable from tuberculous meningitis

• Disseminated infection

  • Children are ill, with fever and hepatosplenomegaly, and organisms are demonstrated in bone lesions, lymph nodes, or liver

  • Between 60% and 80% of patients with AIDS acquired MAC infection in the past, characterized by fever, night sweats, weight loss, and diarrhea

  • Infection usually indicates severe immune dysfunction and is associated with CD4 lymphocyte counts less than 50/μL

  • Infection is very rare due to more effective HIV therapy

Diagnosis

Laboratory Findings

• Mantoux testing

  • Negative or small reaction (< 10 mm) in most cases

  • Larger reactions may be seen particularly with M marinum infection

• Interferon-gamma release assay (IGRA) tests are commonly negative although ...