What is the most common cause of viral diarrhea in AIDS?
CMV is one of the most common opportunistic infections in patients with AIDS, occurring late in the course of HIV infection when immunodeficiency is severe (CD4 lymphocyte count l < 100/mm 3 ). CMV has been identified in mucosal biopsy samples in as many as 45% of patients with AIDS and diarrhea, especially in those patients with negative stool studies. CMV causes both enteritis and colitis. A number of other viral pathogens—adenovirus, rotavirus, astrovirus, picobirnavirus, and coronavirus—have been reported to involve the GI tract in patients with AIDS, but their clinical importance remains to be determined. HSV can cause proctitis that mimics diarrhea because of the rectal mucous discharge. However, HSV does not cause enterocolitis because it invades the squamous mucosa, not the columnar epithelium, such as the one lining the colonic and small bowel mucosa.