A Guide to Mycobacterium Avium Complex (MAC)

Common Bacterial Infection Can Be Deadly In Advanced HIV Disease

Micrographic image of MAC-infected lymph node tissues.. Dr. Edwin P. Ewing, Jr./Centers for Disease Control and Prevention

What Is Mycobacterium Avium Complex?

Mycobacterium avium complex, also known as MAC, is a serious bacterial infection often seen in people with advanced HIV disease. While anyone an be infected with MAC, illness typically only presents in those with severely compromised immune systems.

As such, MAC is classified as an AIDS-defining illness, affecting anywhere from 20-40% of persons with AIDS-associated immune suppression who are not on HIV therapy or taking preventive prophylactic medications.

MAC tends to most commonly affect the lungs, although many of these infections are not considered life-threatening.

However, when a person's CD4 count drops below 50 cell/mL, MAC can move beyond the lungs and involve other major organ systems, including the liver, spleen, and bone marrow. It is then that MAC infection can become severe to life threatening.

What Are the Symptoms of MAC?

MAC infection often occurs in the lungs or intestines and can often present with few, if any, symptoms. However, when into spreads (disseminates) beyond the lungs and into the bloodstream, it can cause widespread infection. Early signs of disseminated MAC include:

  • Fever
  • Night sweats
  • Chills
  • Fatigue (often due to anemia)
  • Diarrhea
  • Weight loss (cachexia)
  • Abdominal pain

How Is MAC Diagnosed?

MAC disease is diagnosed by laboratory tests that can identify the MAC bacteria in samples of blood or bone marrow. Bone marrow samples are usually extracted from the hip bone with a needle, while blood samples are collected a standard blood draw.

The sample are then cultured in test tubes to determine whether the MAC bacteria is there or not. This takes around seven days.

How Do People Get MAC?

MAC organisms live all around us, including the soil, in foods, and in everyday livestock. MAC bacteria can be also found in many sources of drinking water, including treated water systems, and even in household dust.

It is, therefore, very difficult to avoid. On the other hand, MAC does not seem to be passed from one person to person.

How Can I Avoid MAC?

Since the avoidance of MAC is difficult to unlikely, the best way to avoid disease is to ensure that your immune system remains intact. This is best accomplished by treating HIV infection with antiretroviral therapy (ART). The use of ART can not only ensure your immune system remains strong, maintaining higher CD4 counts, it can restore immune function even in persons with moderate to severe immune suppression.

Currently, ART is recommended for all individuals with HIV at the time of diagnosis. Early diagnosis and treatment will not only greatly prevent MAC and other opportunistic infections, it is also associated with longer life and fewer HIV- and non-HIV-related illnesses.

In HIV-positive persons with CD4 counts under 50 cells/mL, daily prophylactic drugs are prescribed to better prevent the development of MAC. The drugs commonly used include:

  • Clarithromycin, a type of antibiotic able to rapidly clear MAC from the blood
  • Azithromycin, considered a good alternative to clarithromycin
  • Rifabutin, another viable alternative (although known to interact with certain HIV drugs)

How Is MAC Treated?

MAC disease is most commonly treated with a combination of clarithromycin and ethambutol, with or without rifabutin. ART would also be initiated for those not yet on therapy.

However, in persons with very low CD4 counts, there is a chance that MAC symptoms may flare up once ART is started. This is a phenomenon known as immune reconstitution inflammatory syndrome (IRIS), in which the compromised immune system is suddenly over-activated, causing an all-body inflammatory response. If this occurs, corticosteroids can be prescribed to treat the IRIS-associated symptoms until the immune response normalizes.

Once the person's CD4 count is over 100 cells/mL and stabilizes above this level for six months, prophylactic treatment can be stopped.

Sources:

National Institutes of Health (NIH). "Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents -Disseminated Mycobacterium avium Complex Disease." Bethesda, Maryland; updated May 17, 2013; accessed May 29, 2016.

U.S. Preventive Services Task Force (USPSTF). "Screening for HIV: U.S. Preventive Services Task Force Recommendation Statement." Rockville, Maryland; April 2013; accessed February 7, 2014.

NIH. "Starting antiretroviral therapy early improves outcomes for HIV-infected individuals." Bethesda, Maryland; issued May 27, 2015.

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