What Is Mycobacterium Avium Complex?

Mycobacterium avium complex (MAC) is a group of bacteria related to tuberculosis. These germs are very common in food, water, and soil. Almost everyone has them in their bodies. When you have a strong immune system, they don't cause problems. But they can make people with weaker immune systems, like those with HIV, very sick.

Because of that, it's considered an opportunistic infection. MAC usually causes problems after HIV becomes AIDS and your CD4 cell count gets lower than 50.

You can prevent MAC by starting antiretroviral therapy (ART) early and not allow your CD4 count to get low.  If you have a low CD4 count and you get MAC, the infection can be treated, but you may need to take MAC drugs for a long time, until your CD4 count increases in response to ART.

Symptoms

It can infect one part of your body, like your lungs, bones, or intestines. This is localized infection. It can also spread and cause disease throughout your body. Your doctor may call that disseminated infection.

If MAC goes all over your body, you may have:

You could also have more serious symptoms like:

Getting a Diagnosis

Many other infections can cause the same symptoms as MAC. Getting the right diagnosis will help you treat it.

In addition to a physical exam, your doctor may order lab tests to find MAC bacteria in your:

  • Blood
  • Urine
  • Sputum (thick fluid made in your airway and lungs)
  • Bone marrow
  • Tissue

The samples your doctor will take will grow for several weeks in a lab. Then a lab technician will check these cultures for signs of MAC.

While waiting for those results, your doctor may order other tests, including blood tests to check for problems such as anemia and liver disease.

A CT scan of your chest and abdomen can help your doctor see problems with your lymph nodes, liver, or spleen.

Your doctor may also take a tissue sample and look it under a microscope. That's called a biopsy.

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Treatment

In addition to starting ART, to fight MAC you'll probably get a combination of antibiotics so your body doesn't become resistant to any one drug. You will likely get either clarithromycin (Biaxin) or azithromycin (Zithromax) plus ethambutol.  Depending on the severity of your infection and your immune status, additional antibiotics that might be needed includes.

After you get the infection under control, you'll switch to maintenance treatment for about 12 months. This treatment generally consists of the same drugs in your initial treatment. 

MAC medications can have side effects, such as:

  • Hearing loss
  • Numbness in feet
  • Headache

MAC drugs may also cause problems with:

Prevention

Because MAC bacteria are so common, it's not really possible to avoid them. Instead, the best way to prevent MAC when you have HIV is to take ART. If you have a low CD4 count, additional drugs to prevent MAC are no longer recommended if you are taking ART that is expected to make the HIV virus in your blood “undetectable.”

If you have a low CD4 count and you get MAC, in addition to your ART you will need to take your MAC medication until your CD4 count increases in response to ART.  If you can keep your CD4 count above 100 for 6 months while on ART, you may be able to stop taking medicine for MAC. But you'll need to start again if your CD4 count goes back down.

WebMD Medical Reference Reviewed by Jonathan E. Kaplan, MD on December 16, 2018

Sources

SOURCES:
AIDS Treatment Data Network: "MAC (Mycobacterium avium complex)."
CDC: "You Can Prevent MAC."
AIDSInfoNet: "Mycobacterium Avium Complex (MAC)."
Clinical Manual for Management of the HIV-Infected Adult, July 2006.
UCSF Center for HIV Information: "Mycobacterium avium Complex and Atypical Mycobacterial Infections in the Setting of HIV Infection."

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