Mycobacterium Avium Complex (MAC) (Mycobacterium Avium-Intracellulare [MAI]) Clinical Presentation

Updated: Dec 15, 2022
  • Author: Janak Koirala, MD, MPH, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Mycobacterium avium complex (MAC) infection usually presents in 1 of 3 forms:

  • Pulmonary MAC infection in immunocompetent hosts

  • Disseminated MAC (DMAC) infection in individuals with advanced AIDS

  • MAC lymphadenitis in children

Pulmonary MAC infection in immunocompetent hosts generally manifests as cough, sputum production, weight loss, fever, lethargy, and night sweats. The onset of symptoms is insidious. Symptoms may be present for weeks to months. Many patients have only a chronic cough with purulent sputum production. Hemoptysis is rare in MAC infection. Less commonly, MAC has been associated with hot-tub lung, a type of hypersensitivity pneumonitis-like lung disease due to exposure to MAC in hot tubs.

Patients with advanced AIDS (generally with CD4 counts < 50 cells/µL) who have DMAC infection commonly present with fever of unknown origin (FUO). Usual signs and symptoms are as follows:

  • Sweating

  • Weight loss

  • Fatigue

  • Diarrhea

  • Shortness of breath

  • Right upper quadrant abdominal pain

In addition, other reported MAC infection manifestations in patients with AIDS have included mastitis, pyomyositis, cutaneous abscess, brain abscess, and GI mycobacteriosis.

Immune reconstitution inflammatory syndrome (IRIS) associated with MAC has been reported in patients with underlying MAC infection. These patients develop symptoms of IRIS shortly after initiating ART unmasking subclinical MAC infection ("unmasking IRIS").

MAC lymphadenitis is predominantly a disease of children aged 1-4 years, primarily involving unilateral cervical lymph nodes. Submandibular and submaxillary lymph nodes are the usual sites, but preauricular, postauricular, and submental nodes also may be affected. Rarely, infection of the axillary, epitrochlear, or inguinal lymph nodes may develop after direct cutaneous inoculation.

The lymph nodes usually enlarge insidiously but may enlarge more rapidly in younger children. The lymphadenitis generally resolves spontaneously, but the lymph nodes also may caseate and rupture through the skin, forming a sinus tract with chronic discharge.

Less commonly, MAC may produce any of the following:

  • Skin and soft-tissue infections

  • Osteomyelitis

  • Peritonitis (in patients with cirrhosis)

  • Bursitis

  • Septic arthritis

  • Tenosynovitis

Any history of the introduction of a foreign object (eg, needle, splinter) should be sought if cutaneous MAC infection is suspected.


Physical Examination

Physical findings in MAC infection depend on the form of infection and the patient. In immunocompetent patients with pulmonary MAC infection, lung crackles, rhonchi, or both generally can be heard on auscultation. Additionally, depending on the type of lung lesion and severity of infection, patients with pulmonary MAC infection may have tachypnea, dullness on chest percussion, or bronchial breath sounds.

DMAC infection in patients with AIDS can cause generalized wasting, skin pallor, tender hepatosplenomegaly, and lymphadenopathy.

Lymphadenitis in children can cause unilateral enlargement of submandibular, preauricular, parotid, and/or postauricular lymph nodes. Involved nodes are usually multiple and rubbery to firm and may appear to be fixed to deeper structures. They may become matted together as the disease progresses. The overlying skin may appear shiny, thin, and erythematous or violaceous. Sinus tracts may be present in advanced cases.

Patients with synovitis may present with pain and swelling of a joint or features of bursitis or tenosynovitis.



Patients with MAC lymphadenitis may develop a sinus tract with drainage.

Patients with cavitary MAC lesions may develop secondary bacterial or fungal infection.

Patients with HIV/AIDS may develop immune reconstitution inflammatory syndrome (IRIS) after initiation of antiretroviral and anti-MAC therapies. The IRIS may mimic worsening of symptoms and paradoxical enlargement of infected lymph nodes ("Paradoxical IRIS").