Mycobacterium avium [MY-co-bak-TEER-ee-um A-vee-um] complex, also known as “MAC,” is the name of a group of germs. These germs can infect people who are living with HIV. Adults with HIV usually don’t get MAC disease until their T-cell count drops below 50. Because MAC disease occurs later in the course of HIV infection, it usually is not the first sickness a person with HIV gets. Most people with HIV have already been diagnosed with AIDS before they get MAC. About 20 to 30 percent of people with AIDS get MAC disease.

Yes. The risk of MAC for children with HIV goes up as their T-cell count goes down, just as it does for adults. However, children who get MAC disease usually get it before their T-cell count falls to 50. Children with HIV usually have higher T-cell counts than adults with HIV.

Although MAC usually infects persons through their lungs or intestines, it spreads quickly through the bloodstream, causing widespread or "disseminated" disease. People with disseminated MAC disease can have fever, night sweats, weight loss, abdominal pain, tiredness, and diarrhea.

MAC disease is diagnosed by laboratory tests that can identify the MAC germ in samples of blood, bone marrow, or tissue.

People with AIDS probably get MAC disease through normal contact with air, food, and water. MAC disease has been found in many types of animals, including birds, chickens, pigs, cows, rabbits, and dogs. MAC germs can be found in most sources of drinking water, including treated water systems, and in dirt and household dust. MAC disease does not seem to be spread from one person to another.

Because MAC germs are found in food, water, and soil, there is no easy way to avoid them. However, there are drugs that can prevent MAC germs from causing disease.

Because MAC disease occurs in people with very low T-cell counts, you should not get treatment to prevent MAC disease until your T-cell count is below 50. Your doctor will tell you when you or your child need to begin treatment for preventing MAC disease.

Drugs which can reduce your chances of getting MAC disease are

• clarithromycin [kla-REE-thro-MY-sin]

• azithromycin [a-ZEE-thro-MY-sin]

• rifabutin [rif-a-BU-tin]

Ask your doctor whether you should take one of these drugs.

Yes. Rifabutin can cause eye irritation. If you are taking rifabutin or other drugs to prevent MAC, see your doctor regularly and report any side effects.

Yes. If you have had MAC disease, continue to take drugs to treat and prevent further MAC disease. MAC disease is most commonly treated with a combination of clarithromycin and ethambutol [eth-AM-bu-tol], with or without rifabutin.