24 yrs old AIDS patient develops chronic abdominal pain, low grade fever, diarrhea, and malabsorption. Oocyst demonstrated in stool. Likely cause of his diarrhea is –
**Core Concept**
The patient's symptoms, including chronic abdominal pain, low-grade fever, diarrhea, and malabsorption, are suggestive of a chronic gastrointestinal infection. The presence of oocysts in the stool indicates a protozoal infection.
**Why the Correct Answer is Right**
The patient's symptoms are consistent with intestinal cryptosporidiosis, a parasitic infection caused by the protozoan *Cryptosporidium parvum*. This infection is particularly severe in immunocompromised individuals, such as those with AIDS. The oocysts are ingested and undergo sporulation in the gastrointestinal tract, leading to invasion of the intestinal epithelial cells and subsequent malabsorption and diarrhea.
**Why Each Wrong Option is Incorrect**
**Option A:** Giardiasis is caused by the protozoan *Giardia lamblia*, which typically presents with watery diarrhea, but not necessarily malabsorption or chronic abdominal pain.
**Option B:** Cytomegalovirus (CMV) colitis is a viral infection that can cause diarrhea, but it is not typically associated with oocysts in the stool.
**Option C:** Microsporidiosis is another parasitic infection that can cause diarrhea in immunocompromised individuals, but it is more commonly associated with *Enterocytozoon bieneusi*.
**Clinical Pearl / High-Yield Fact**
Immunocompromised patients with chronic diarrhea should be evaluated for opportunistic infections, including cryptosporidiosis, microsporidiosis, and CMV colitis.
**Correct Answer: C. Cryptosporidiosis**