Mycobacterium avium complex infection

Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) infection is a type of bacterial infection caused by non-tuberculous mycobacteria, primarily affecting individuals with compromised immune systems. The Mycobacterium avium complex consists of two main species: *Mycobacterium avium* and *Mycobacterium intracellulare*. These bacteria are ubiquitous in the environment and can be found in soil, water, and dust.

Pathophysiology

MAC infections occur when the bacteria are inhaled or ingested, leading to colonization and infection. In immunocompetent individuals, the immune system typically controls the infection, preventing disease. However, in immunocompromised individuals, such as those with HIV/AIDS, the bacteria can cause disseminated disease. The infection can affect various organs, including the lungs, lymph nodes, and gastrointestinal tract.

Clinical Manifestations

The clinical presentation of MAC infection varies depending on the site of infection and the immune status of the host. Common symptoms include:

• Pulmonary MAC infection: Chronic cough, sputum production, weight loss, and fatigue. It can mimic tuberculosis in its presentation.
• Disseminated MAC infection: Fever, night sweats, weight loss, and anemia. This form is more common in patients with advanced HIV infection.
• Lymphadenitis: Swelling of the lymph nodes, particularly in children.

Diagnosis

Diagnosis of MAC infection involves a combination of clinical, radiological, and microbiological criteria. Key diagnostic methods include:

• Sputum culture: Isolation of MAC from respiratory specimens.
• Blood culture: Useful in disseminated disease.
• Imaging studies: Chest X-rays or CT scans to identify pulmonary involvement.
• Histopathology: Biopsy of affected tissues may show granulomatous inflammation.

Treatment

Treatment of MAC infection typically involves a combination of antibiotics over an extended period. The standard regimen includes:

• Clarithromycin or azithromycin: As the cornerstone of therapy.
• Ethambutol: To prevent resistance.
• Rifampin or rifabutin: As an additional agent.

The duration of treatment is usually 12 months after culture conversion. In patients with HIV, antiretroviral therapy is also crucial to improve immune function.

Prevention

Preventive measures for MAC infection focus on reducing exposure to the bacteria and enhancing immune function. In HIV-infected individuals, prophylactic antibiotics such as azithromycin or clarithromycin may be used when CD4 counts fall below 50 cells/mm³.

Prognosis

The prognosis of MAC infection depends on the immune status of the patient and the timeliness of treatment. With appropriate therapy, many patients can achieve clinical improvement and microbiological clearance.

Also see

• Non-tuberculous mycobacteria
• HIV/AIDS
• Tuberculosis
• Antibiotic therapy