Mycobacterium Avium Complex - Causes, Symptoms and Treatment

Definition:

Mycobacterium avium complex (MAC) is a serious opportunistic bacterial infection which most commonly affects patients in the advanced stages of acquired immunodeficiency syndrome (AIDS). In patients with AIDS, MAC is usually disseminated and affects those with CD4+ T-cell counts below 50/mm 3 .Any organ system can he involved, especially those with many mononuclear phagoeytes (such as the liver, spleen, and bone marrow). Less commonly, MAC may produce pulmonary disease in non-immunocompromised people; it may manifest in children as cervical lymphadenitis.

The incidence of MAC is not reportable; however, population-based data available for the Houston and Atlanta metropolitan areas suggest a rate of 1 : 100,000 cases per year. Incidence is decreasing among those with human immunodeficiency virus (HIV) as a result of chemoprophylaxis and combination antiretroviral therapy.

Causes of Mycobacterium Avium Complex

The etiologic agents responsible for MAC are Mycobacterium avium and Mycobacterium intracellulare. MAC is a water and soil saprophyte and enters the body through either the GI or respiratory tracts. It is unclear whether active infection results from recently acquired microbes or from reactivation of latent infection. There are no current recommendations regarding avoidance of exposure.

Signs and Symptoms of Mycobacterium Avium Complex

The signs and symptoms of MAC are generally nonspecific and include fever, night sweats, weight loss, weakness, anorexia, diarrhea, malabsorption, and abdominal pain. Enlargement of the liver and spleen is common. Laboratory findings include anemia, neutropenia, and elevated alkaline phosphatase levels. Respiratory symptoms are uncommon in AIDS-related MAC infection. MAC is usually asymptomatic in patients with CD4+ T-cell counts above 100/mm 3.

Diagnosis for Mycobacterium Avium Complex

Blood and bone marrow cultures are the most sensitive diagnostic tests. Disseminated MAC can be diagnosed from one positive blood culture. A positive sputum or stool culture may precede the development of symptomatic disease but may also represent colonization rather than infection. A history of prior opportunistic diseases is usually present.

Other diagnostic tests may include a chest radiograph, dilated eye exam, liver function tests, hepatitis profile, lymph node aspiration, test for cryptococcal antigen, purified protein derivative (PPD) and controls, coccidioidomycosis serologies, and histoplasma antigen.

Treatment for Mycobacterium Avium Complex

There is currently no standard therapy for MAC; however, guidelines published by the U.S. Public Health Service and Infectious Diseases Society of America recommend a combination treatment regimen which includes at least two drugs, one of which should be either clarithromycin or azithromycin. Ethambutal is a secondline drug; clofazimine, rifabutin, rifampin, amikacin, and ciprofloxacin are third-line drugs. Clinical and microscopic response is usually evident in 4 to 6 weeks. At this time, treatment is considered to be lifelong. Treatment should also include preventing further infection and reducing the risks of opportunistic infections.

Special Considerations and Prevention Tips for Mycobacterium Avium Complex

• Stress the importance of compliance with thc medication regime to prevent life-threatening MAC infection.
• Other areas of education should include general lifestyle modifications such as smoking cessation, good nutrition, and regular exercise to enhance quality of life, since so many HIV-infected patients are now living long enough to encounter the chronic diseases found in the general population.
• Use proper personal protective gear when obtaining or handling laboratory samples.
• Some practitioners also advocate prophylactic treatment for MAC in patients with HIV whose CD4+ T-cell counts are below 100/mm 3 . Generally, rifabutin, clarithromycin, or azithromycin are used.
• Monitor carefully for drug adverse effects; most are minor and include GI symptoms. Be alert for signs of nephro- and ototoxicity (amikacin), pain or tingling of the extremities and yellow skin discoloration (clofazimine), visual disturbances (ethambutol), and anemia (rifabutin).
• Monitor nutritional status.
• Administer antipyretics and antipyretics as needed.
• Frequently monitor CD4+ T-cell counts.