What Are Mycobacterium Avium Complex Infections? Causes, Treatment, Prevention, and More

Mycobacterium avium complex, also called MAC, is a group of bacteria that can cause life-threatening infections in people with severely compromised immune systems.

MAC consists of two types of nontuberculous mycobacteria: Mycobacterium avium and Mycobacterium intracellulare. These bacteria are generally indistinguishable by scientists, so they are often grouped together as mycobacterium avium complex.

MAC is everywhere in the environment and does not make most people with normally functioning immune systems sick, though that is possible.

Learn more about the types, symptoms, risk factors, and treatment options available for mycobacterium avium complex infections.

There are three main types of mycobacterium avium complex infections. These include: (1)

• Pulmonary MAC infections affect the lungs. This is the most common type of MAC infection and mainly affects people who have lung disease.
• Disseminated MAC infections occur when the infections have spread throughout the body. This type of infection is typically seen in those living with advanced AIDS.
• MAC-associated lymphadenitis is a MAC infection that causes swelling of the lymph nodes, or small structures throughout the body that work as filters for harmful substances. MAC-associated lymphadenitis usually affects lymph nodes in the neck. This type is most common in young children.

Symptoms of MAC infections will vary depending on the type of infection and area of the body affected.

Signs of pulmonary mycobacterium avium complex infections start slow and gradually get worse over time. These can include:

• Cough
• Weight loss
• Fever
• Fatigue
• Night sweats

Symptoms of disseminated mycobacterium avium complex infections can include:

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

Other, less common symptoms of disseminated mycobacterium avium complex infections include skin or brain abscesses, mastitis (infection of the breast tissue), and pyomyositis (infection of the skeletal muscle).

MAC-associated lymphadenitis typically manifests by causing lymph nodes — particularly those in the neck — to swell.

MAC is ubiquitous in the environment and can be found in soil, dust, water, and food. It is thought to enter the body through the air when people breathe or when they swallow water. Mycobacterium avium complex will not make most people with a healthy immune system sick.

It is an opportunistic infection, meaning it occurs when a pathogen takes advantage of a person without a normally functioning immune system. So while many people have MAC in their bodies, it almost always will only cause an infection in those with a very weakened immune system.

The biggest risk factor is having a compromised immune system. Most people who get MAC infections are those living with HIV/AIDS, certain cancers, and lung diseases like chronic obstructive pulmonary disease, cystic fibrosis, or bronchitis.

In people with HIV, MAC infections are more likely to occur in those with low CD4 counts, which is a measure of lymphocyte cells in the blood that are an important indicator of the immune system’s strength.

While mycobacterium avium complex infections are not inherited — a person must be exposed to one of the associated types of bacteria in order to get sick — there have been several reports of more than one family member becoming ill with a MAC infection. In these instances, scientists believe that there is a variation in the gene or genes involved in the immune response. Such a variant could make some people more likely to get an infection than others. But many genes are involved in the immune response, and researchers have yet to identify a single gene responsible for MAC infections.

Older people are also a risk group for MAC infections. (1)

A doctor will diagnose MAC infections based on a number of tests, including a physical examination, lab test results, X-rays, and CT scans. Since symptoms are similar to other types of infections, various causes will need to be ruled out.

One of the laboratory tests may include a culture of sputum, or mucus spit up from the lungs. The test involves placing cells from the sputum sample in an environment that encourages bacteria to grow. It may take several days to see if the sample tests positive for pulmonary MAC. A staining test of a sputum sample called an acid-fast bacillus test may also be performed to help identify the bacteria under a microscope. (2)

Disseminated MAC infections are diagnosed with cultures of blood and lymph node cells that are tested for the presence of MAC bacteria. Urine, stool, liver, and bone marrow cultures may also be used to diagnose MAC infections. A CT scan might be done to help determine the sites of the body that the MAC infection has affected.

MAC-associated lymphadenitis is diagnosed with a positive finding of the bacteria in the culture of lymph node cells. When lymph nodes are swollen, a biopsy is taken to collect the cells to be tested. (1,3)

Treatment for mycobacterium avium complex infections varies depending on the type of MAC infection (pulmonary, disseminated, or MAC-associated lymphadenitis), as well as if the patient has other medical conditions, including HIV/AIDS, COPD, or cancer.

Pulmonary and disseminated MAC infections are typically treated the same way, with a three-drug combination of antibiotics: azithromycin (Zithromax), rifampin (Rifadin), and ethambutol (Myambutol). (1)

Three types of antibiotics are usually used because MAC bacteria can very easily become resistant to certain types of antibiotics, and the combination approach reduces the chance that the bacteria will come back after treatment.

These drug treatment regimens are long-term and can last up to 15 to 18 months. (4)

In 2018, the FDA approved a drug called liposomal amikacin (Arikayce) to treat MAC-associated lung disease as part of a combination antibacterial drug regimen in people who continue to test positive for MAC bacteria after six consecutive months of treatment.

Patients living with HIV/AIDS who have mycobacterium avium complex infections are treated with antibiotics and antiviral medications to treat the HIV infection.

For those with a pulmonary MAC infection who have not responded well to antibiotics, surgery to remove a single spot of infection may be suggested. Surgery is typically only done when MAC bacteria is found in only one lung and the procedure is deemed to cause no lasting harm.

Treatment of MAC-associated lymphadenitis often involves surgical removal of the affected lymph nodes. Antibiotics may also be prescribed. In many children, MAC-associated lymphadenitis will not negatively affect their health and may even go away on its own without treatment. (1)

The long-term health outcomes for people with mycobacterium avium complex infections depends on the type of MAC infection an individual has and if there are any other medical conditions present.

People who are HIV-positive may have a shorter life span depending on the strength of their immune system and response to antiviral medications. Even if treatment is successful, MAC infections can return over time, so people who have had these infections need to continue to be monitored.

For individuals with lung disease from a MAC infection who do not have HIV, studies show a range of treatment success rates from 20 to 90 percent.

According to a systematic review published in 2018, the survival rate for people with pulmonary MAC infections without other diseases is 75 percent. This means those individuals have a 75 percent chance of still being alive five years after diagnosis. (5)

Some people with mycobacterium avium complex infections may want to look into clinical trials as a possibility for treatment. These are research studies in which people volunteer to test new treatments for diseases.

For more information on clinical trials for MAC infections, visit ClinicalTrials.gov. There you can learn more information about the trial, what intervention is being tested, and locations where it is offered. Talk to your doctor if you are interested in entering a clinical trial.

A healthy diet and regular daily exercise, including walking, yoga, Pilates, and strength training, are highly recommended for people with MAC infections. These lifestyle choices can help with overall health and lessen the fatigue that often accompanies the infections.

Having a strong support network of family and friends can greatly help with recovery from a MAC infection. It is important that loved ones understand what a MAC infection is, what the treatments are, and the side effects of medications. Patients are encouraged to have open and honest conversations with their family about their illness and what they need.

Joining a MAC support group can also be beneficial and promote a core sense of understanding the illness. Others who are living with MAC infections will share their experiences, and many find the process to be therapeutic. Ask your doctor for suggestions if you would like to attend a MAC support group. (4)