The Safety and Effectiveness of Clarithromycin and Rifabutin Used Alone or in Combination to Prevent Mycobacterium Avium Complex (MAC) or Disseminated MAC Disease in HIV-Infected Patients

Inclusion Criteria Concurrent Medication: Recommended: * PCP prophylaxis. Allowed: * GM-CSF or G-CSF. * Erythropoietin. * Therapies (including antiretrovirals) available through expanded access or treatment IND programs. * Other non-experimental therapies available by prescription. * Antihistamines other than those specifically excluded. Patients must have: * Evidence or diagnosis of HIV infection or a history of an AIDS-defining condition by CDC criteria. * CD4 count \<= 100 cells/mm3 within 90 days prior to study entry. * Two baseline blood sample cultures negative for MAC within 30 days of study entry. * No suspected disseminated MAC disease, in the opinion of the clinician. NOTE: * Patients with elevated GGT and/or triglycerides are allowed. NOTE: * Patients may co-enroll on ACTG 081/981/181, ACTG 175, ACTG 204, ACTG 193, ACTG 241, or other acceptable protocols. Exclusion Criteria Co-existing Condition: Patients with the following symptoms or conditions are excluded: * Known or suspected tuberculous infection or other non-tuberculous mycobacterial infection requiring chemotherapy or chemoprophylaxis (with the exception of isoniazid prophylaxis alone). NOTE: * Patients may enroll who successfully completed tuberculosis (TB) treatment and have been off anti-TB drugs for more than 6 months with no symptoms of mycobacterial infection. * Active TB. * Known hypersensitivity to study drugs. * Malabsorption as defined by persistent diarrhea with more than 8 stools per day for \> 6 weeks. Concurrent Medication: Excluded: * Frequent (more than once per month), repeated, or continuous treatment courses of quinolones, erythromycin, spiramycin, azithromycin, clarithromycin, or clindamycin. * Concomitant terfenadine or astemizole. Prior Medication: Excluded: * Prophylaxis with azithromycin, clarithromycin, or rifabutin for more than 4 months.