A 34-year-old man comes to the office due to severe diarrhea and light-headedness. The diarrhea started approximately 14 days ago and is associated with malaise, nausea, and abdominal cramps. Since then, the patient has had 8-10 watery, nonbloody stools daily and believes he has lost weight. He has a history of HIV infection and has been noncompliant with his medication regimen. The patient's CD4 count was 94/mm³ last month. He recently started working at a horse breeding farm. The patient has not traveled outside of the United States. Temperature is 38.0 C (100.4 F), blood pressure is 108/72 mm Hg, and pulse is 104/min. BMI is 18 kg/m². Mucous membranes are dry. Bowel sounds are increased. Stool is brown and negative for occult blood. Which of the following is the most likely organism responsible for this patient's condition?

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Quizplus · Accepted Answer

11ec25c8_d442_62f0_bc81_e92637629769_MD0003_00 Diarrhea is common in patients with AIDS, especially in those with CD4 counts <100/mm³. In this patient with a recent CD4 count of 94/mm³, severe watery diarrhea, weight loss, and low grade fevers, cryptosporidiosis is the most likely diagnosis. Cryptosporidium is among the most common causes of infectious diarrhea worldwide and is commonly spread through drinking water, animal contact (eg, horse breeding), and person-to-person contact. The pathogen is usually self-limited in immunocompetent hosts, but it may cause severe chronic infection in patients with AIDS (particularly those with CD4 counts <180/mm³). Stool examination with modified acid-fast stain reveals cryptosporidial oocytes measuring 4-6 µm. The mainstay of treatment is supportive care and antiretroviral therapy because infection often persists until CD4 counts improve. (Choice B) Cytomegalovirus (CMV) is a common cause of colitis, esophagitis, or retinitis in patients with AIDS. However, colonic symptoms typically include frequent, small volume stools that are often bloody. CMV gastrointestinal symptoms typically occur with CD4 count <50/mm³. (Choice C) Entamoeba histolytica infection presents with dysentery, which is characterized by abdominal pain, diarrhea, and bloody stools. (Choice D) Disseminated Mycobacterium avium complex infection occurs almost exclusively in patients with severely suppressed CD4 counts (<50/mm³). It most commonly presents with high-grade fevers (>39 C [102.2 F]), weight loss, cough, and diarrhea. (Choice E) Strongyloides stercoralis infection is associated with cutaneous (pruritus and urticaria), pulmonary, and gastrointestinal symptoms. It would be an unlikely cause of this patient's symptoms. Educational objective: Cryptosporidium parvum is a major cause of chronic diarrhea in patients with HIV who have CD4 counts <180/mm³.

A 34-Year-Old Man Comes to the Office Due to Severe