MAC is a group of mycobacteria found in the air, water, soil, household dust, food, drinking water (even from treated water systems) and in many animals. These bugs are related to both bacteria and fungi; some are capable of causing serious human illness (tuberculosis and leprosy are caused by mycobacterium, for example). They can enter the body through the lungs or intestines and then spread through the bloodstream.
MAC occurs most frequently among people with HIV/AIDS (although its incidence in that group has been declining) but in rare cases, also infects people who don't have compromised immunity, including children. According to the CDC, MAC occurs in approximately one out of every 100,000 persons in the United States per year. It isn't passed from person to person and is probably picked up from the environment, although just how isn't known. Symptoms include high fever, night sweats, diarrhea, weight loss, abdominal pain, fatigue, weakness, anemia, elevated liver function tests and, sometimes, enlargement of the liver and spleen.
MAC is treated with a combination of antibiotics that should include at least two drugs, usually clarithromycin or azithromycin, plus ethambutol. Other antibiotics may be added depending on the severity of the case. Unfortunately, all of the drugs used to treat MAC can cause serious side effects that may require treatment with yet other drugs. And, because the infection is difficult to eradicate, the antibiotics have to be used long term to prevent further attacks.
In addition to antibiotic therapy, I would recommend trying to increase resistance to infection by boosting daily intake of garlic and medicinal mushrooms (especially shiitake, enoki, maitake, reishi and cordyceps). Your wife might also consult with a practitioner of traditional Chinese medicine to help address her immunity and MAC.
Andrew Weil, M.D.