Mutually monogamous sexual relationship A

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relationship in which each partner agrees to be


myalgia Tenderness or pain in a muscle or muscles.

Mycelex G See clotrimazole.

mycobacteriosis An infection caused by any mycobacterium.

Mycobacterium A genus of acid-fast organisms of the Mycobacteriaceae family, which includes the causative organisms of tuberculosis, leprosy, and mac. The term acid-fast refers to a property of mycobacteria on staining done in microbiology labs, namely, that these bacteria do not decolorize when dilute acid is applied to the slide.

Mycobacterium avium complex (MAC) A serious bacterial infection that causes systemic infection in immunosuppressed persons and lung disease in persons with underlying chronic lung disease. of unprecedented frequency in persons with AIDS, MAC is the most common bacterial opportunistic infection of people who have advanced HIV disease. It is also one of the last opportunistic infections to develop.

MAC is caused by two species of bacteria, Mycobacterium avium and Mycobacterium intracellu-lare, which are collectively referred to as Mycobacterium avium complex. Both M. avium and M. intracellulare are closely related to M. tuberculosis, the bacterium that causes TB. MAC bacteria are found commonly in nature and probably enter the body by inhalation of dust and during the consumption of food and water. The infection is not transmitted from person to person, so MAC patients need not be isolated as HIV-infected patients with active TB must. MAC infection is thought to begin in the intestines. The bacteria then spread from there to the lymph nodes, blood, and other organs of the body. Generally, infection becomes apparent when the CD4 lymphocyte count drops below 50 cells/mm, and cell counts as low as 10 cells/mm are common at the time of MAC diagnosis.

The bacteria responsible for MAC are commonly found in food, water, and the environment. To date, there are no recommendations for avoiding exposure.

Symptoms of MAC include fever, malaise, weight loss, chronic diarrhea, and abdominal pain. The infection can interfere with the absorption of food and nutrients from the intestines, thereby contributing to malnutrition and wasting during late-stage disease.

MAC can be localized (limited to a specific organ or area of the body) or disseminated throughout the body. Disseminated MAC infection affects a variety of organs, including the lungs, liver, spleen, lymph nodes, bone marrow, intestines, and blood. MAC infection is found almost exclusively in people with HIV disease; it rarely occurs in people who are immune-suppressed for other reasons. Note that as children live longer with HIV disease, MAC occurs with increasing frequency. It is an indicator of markedly advanced disease and requires treatment with multiple drugs.

The development of highly effective MAC prophylaxis has been a major advance in the treatment of HIV infection. New therapies offer promise for both prevention and treatment. At present, the drug azithromycin is preferred for prophylaxis, and the related drug clarithromycin for treatment of MAC illness. Individuals who cannot tolerate azithromycin or clarithromycin can take rifabutin. Prophylaxis is generally given when the CD4 lymphocyte count drops below 50 cells/mm and stopped if CD4 count rises and remains above 50-100 cells/mm. Therapy generally includes clar-ithromycin (without which treatment is much less effective), ethambutol, and one other drug (usually rifabutin or ciprofloxacin). Alternatives for prophylaxis are clarithromycin and rifabutin. MAC may become resistant to therapy if patients do not take the full doses of the anti-MAC drugs. Studies are needed to ascertain potential drug interactions and toxicities.

The presence of disseminated MAC should be ruled out before prophylaxis is started. If disease is present, multidrug therapy is used to treat it, whereas prophylaxis requires only one drug. If only one drug is given to treat the disease, drug resistance may develop. Similarly, TB should be ruled out in individuals who are receiving rifabutin

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