A 26-year-old woman comes to the emergency department due to 3 weeks of fever, watery diarrhea, nausea, abdominal cramps, and weight loss of 4.5 kg (10 lb). She has a history of AIDS and is noncompliant with therapy. The patient has been admitted to the hospital twice in the last 4 months due to Pneumocystis pneumonia. Temperature is 38.2 C (100.8 F), blood pressure is 102/62 mm Hg, and pulse is 102/min. BMI is 18 kg/m². Scattered lymphadenopathy is present in the cervical, axillary, and inguinal chains. Abdominal examination reveals mild, diffuse tenderness and no organomegaly. CD4 count is 18/mm³ and alkaline phosphatase is 484 U/L. Blood cultures in specialized media grow nontuberculous mycobacteria. Which of the following is the most appropriate antibiotic therapy for this patient?

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11ec25c8_d456_1226_bc81_4bd104d6348f_MD0003_00 This patient with untreated AIDS has subacute fever, weight loss, gastrointestinal symptoms, and positive blood cultures for nontuberculous mycobacteria, indicating disseminated Mycobacterium avium complex (MAC). MAC is caused by the ubiquitous nontuberculous mycobacteria, M avium and Mycobacterium intracellulare. Patients with AIDS who have CD4 counts <50/mm³ are at greatest risk. Manifestations include nonspecific systemic symptoms (eg, fever, cough, abdominal pain, diarrhea, night sweats, weight loss), lymphadenopathy, and an elevated alkaline phosphatase level (reflecting hepatic involvement). Hepatosplenomegaly can also occur. MAC is diagnosed with blood cultures or bone marrow aspirate. First-line treatment includes a macrolide (eg, clarithromycin, azithromycin) combined with ethambutol. Antiretroviral therapy should also be initiated a few days after MAC therapy begins. In the past, patients with untreated AIDS who had CD4 counts <50/mm³ were given primary prophylaxis (azithromycin) to prevent MAC infections, but this is no longer recommended due to cost, low overall risk, and concern for antimicrobial resistance. (Choice A) Trimethoprim-dapsone is an alternative treatment regimen for Pneumocystis pneumonia (PCP). Although this patient is at high risk for PCP due to a lack of antimicrobial prophylaxis, most cases present with progressive respiratory distress, hypoxia, dry cough, and fever. Blood cultures would not grow nontuberculous mycobacteria, and alkaline phosphatase elevation and diarrhea would be atypical. (Choice B) Isoniazid-based combination therapy is the mainstay of Mycobacterium tuberculosis treatment. Although patients with AIDS are at much greater risk for infection/disseminated disease, the presence of circulating nontuberculous mycobacteria indicates MAC, rather than M tuberculosis, infection. (Choice D) Metronidazole-based combination therapy is used to treat Entamoeba histolytica infections. Although patients with AIDS are at increased risk for invasive amebiasis and many cases present with abdominal pain, fever, diarrhea, and weight loss, the presence of nontuberculous mycobacteria in the bloodstream makes MAC far more likely. (Choice E) Pyrimethamine-based combination therapy is used to treat toxoplasmosis, which usually causes encephalitis in patients with AIDS. Although pulmonary or gastrointestinal infection can occasionally occur, nontuberculous mycobacteria would not be seen on blood culture. Educational objective: Mycobacterium avium complex is seen primarily in patients with advanced AIDS (CD4 <50/mm³). It is caused by the nontuberculous mycobacterium, M avium or Mycobacterium intracellulare. Patients usually have nonspecific symptoms (eg, diarrhea, weight loss), an elevated alkaline phosphatase level, and lymphadenopathy. Diagnosis is typically made with blood culture or bone marrow aspirate; treatment with macrolide-based combination therapy is curative, but antiretroviral therapy should be initiated to prevent future infection. References: Prevention and treatment of opportunistic infections in HIV-infected adults and adolescents: updated guidelines from the Centers for Disease Control and Prevention, National Institutes of Health, and HIV Medicine Association of the Infectious Diseases Society of America. (http://www.ncbi.nlm.nih.gov/pubmed/24585567)

A 26-Year-Old Woman Comes to the Emergency Department Due to 3