A 30-year-old HIV-positive man with CD4 count of 150 cells/mm³ develops a chronic, watery, profuse diarrhoea that is unresponsive to standard antibiotics. Stool microscopy with modified ZN stain shows small oocysts (4-6 µm). What is the most likely causative organism?
- A Cryptosporidium parvum ✓
- B Giardia lamblia
- C Cyclospora cayetanensis
- D Isospora belli
Correct answer: A. Cryptosporidium parvum
Explanation
Cryptosporidium parvum causes profuse, watery, non-bloody diarrhoea that is particularly severe and life-threatening in immunocompromised patients (CD4 < 200 cells/mm³). Oocysts are small (4–6 µm), acid-fast on modified ZN stain, and are the infective stage transmitted via the fecal-oral route, often through contaminated water. It is the most common opportunistic intestinal protozoan in HIV/AIDS patients in India.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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