Mycobacterium Avium Complex infections

Other Names: Mycobacterium Avium-Intracellulare; MAI; Mycobacterium Avium; Mycobacterium Avium-Intracellulare infection

Mycobacterium avium complex (MAC) refers to infections caused by two types of bacteria: Mycobacterium avium and Mycobacterium intracellulare.

Risk factors

MAC bacteria do not make most people sick. However, people with immune systems that do not work well (from HIV/AIDS or certain cancers for example) or people with lung disease (such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis) are at the greatest risk for getting sick from MAC Infections. Elderly women are also at higher risk to get sick from MAC infections.

Types

There are 3 types of MAC infections. Pulmonary MAC infections - Affect the lungs and are the most common type. These mainly affect elderly women and people who already have lung disease. Disseminated MAC infections - Have spread throughout the body. This type is usually seen in people with advanced AIDS. MAC-associated lymphadenitis - Causes swelling of the lymph nodes (especially in the neck) and is the most common in young children who have normal immune systems.

Cause

Mycobacterium avium complex (MAC) infections are caused by two types of bacteria: Mycobacterium avium and Mycobacterium intracellulare.These bacteria are found in many places including water (fresh or salt), household dust, and soil. MAC bacteria get into the body when the bacteria are inhaled into the lungs or swallowed. Most people have MAC bacteria in their bodies and never get sick. MAC bacteria primarily cause illness in people who have poorly working immune systems or lung disease. Touching the same objects or having a close relationship with people who are sick from a MAC infection does not seem to increase the chance of getting sick. MAC infections are not thought to be contagious from one person to another.

Inheritance

Mycobacterium avium complex (MAC) infection is caused by bacteria and is not an inherited condition. To become infected with MAC bacteria and get sick, a person must first be exposed to one of the associated types of bacteria. It is thought that there is a variation in a gene or genes involved with the body's immune response. A genetic variant in an immune system gene may make some people more likely to get sick from an infection than others. There are many genes involved in the human immune response, and there is no single gene known to be responsible for MAC infections.

Symptoms

While the symptoms are different for each type of infection, general symptoms include fever, night sweats, weight loss, and fatigue. Mycobacterium avium complex infections can cause various symptoms depending on the site of the infection. For example, pulmonary MAC mainly affects the lungs; disseminated MAC affects the whole body; and MAC lymphadenitis causes swollen lymph nodes. The symptoms of pulmonary MAC infection start slowly, get worse over time and may last for weeks to months. People with pulmonary MAC infections may experience cough, weight loss, fever, fatigue, and night sweats. Symptoms of disseminated MAC infection include:

• Fever
• Sweating
• Weight loss
• Fatigue
• Diarrhea
• Shortness of breath
• Abdominal pain
• Anemia

People with disseminated MAC infection may also have symptoms associated with an infection of the breast tissue (mastitis); an infection of the skeletal muscle (pyomyositis), abscesses of the skin or brain, and gastrointestinal problems. MAC lymphadenitis generally affects children with normal immune systems. Symptoms of MAC lymphadenitis usually only include swollen lymph nodes mainly on one side of the neck.

Diagnosis

combination of physical exam findings, laboratory test results, and lung x-rays or CT scan results. The laboratory tests include cultures of mucus spit up from the lungs (sputumand special staining (acid-fast bacillus test). A laboratory culture involves placing cells from a sputum sample in an environment that encourages the bacteria to grow. Results identifying the bacteria may take several days or longer.

Because the symptoms of MAC infections are similar to those of other types of infections, other types of infections and diseases must also be ruled out. Diagnosis of disseminated MAC infection is suspected based on symptoms and is confirmed in cultures of blood and often lymph node cells. Cultures of cells from urine, stool, liver or bone marrow may also be helpful.

CT scans may be used to try to determine the different sites of infection in the body. If pulmonary or disseminated MAC infection is suspected, an HIV test may be done, as well as other tests, to rule out other associated medical conditions. A diagnosis of MAC lymphadenitis is confirmed by finding the bacteria in the culture of lymph node cells. These cells are collected by a biopsy of a swollen lymph node.

Treatment

Treatment options for MAC infections vary by type of infection and by the presence of other medical conditions such as AIDS, cystic fibrosis, COPD, or cancer. Pulmonary MAC infections and disseminated MAC infections are usually treated with a combination of antibiotic medications. There are many types of antibiotics approved for treating MAC infections A combination of medicines is used because some of the disease-causing bacteria can be resistant to certain types of antibiotics. Using more than one antibiotic reduces the chance for the MAC bacteria to come back after treatment is over.

For people who have both HIV/AIDS and a MAC infection, treatment usually involves a combination of different antibiotics for the MAC infection and antiretroviral therapy to treat the HIV infection. In special circumstances, there is some evidence to suggest that surgery to remove a single spot of infection in one lung can be helpful in people who have had a poor response to drug therapy. Surgery is usually only done when the infection is found in only one lung and the surgery won't cause any long-term harm. Treatment of MAC lymphadenitis usually involves surgical removal of affected lymph nodes. Antibiotics may also be prescribed depending on the severity of infection and the response to surgery. The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

• Liposomal amikacin (Brand name: Arikayce)liposomal amikacin (Arikayce) was approved for the treatment of Mycobacterium avium complex (MAC) lung disease as part of a combination antibacterial drug regimen in patients who do not achieve negative sputum cultures after a minimum of 6 consecutive months of a multidrug background regimen therapy.

Prognosis

People who are HIV-positive with MAC infections may have a shortened lifespan depending on their immune systems and their response to HIV medications. In HIV-negative people with lung disease from a MAC infection, the treatment success rates range from 20-90% in different studies. People with certain types of lung disease, people who are underweight, and people with anemia are more likely to have a poor outcome than other HIV-negative people affected by a MAC infection. MAC lymphadenitis in children generally does not impact their health. In some cases, the condition may go away even without treatment. Mycobacterium avium Complex at the US National Library of Medicine Medical Subject Headings (MeSH)