A patient with diarrhea has a fecal smear that is negative for leukocytes. The patient's diarrhea is most likely caused by
The enterotoxigenic strain of Escherichia coli secretes a heat-labile toxin that stimulates adenylate cyclase, producing a cholera-like syndrome that is responsible for the majority of cases of traveler's diarrhea. Because the bowel mucosa is not invaded and there is no toxin-induced damage, the fecal smear is negative for leukocytes. Campylobacter enteritis, shigellosis, ty­phoid fever, and amebiasis are all invasive, and infected individuals have stools with inflammatory cells. Ty­phoid fever is unique because the inflammatory cells are not neutrophils, but mononuclear cells.
Campylobacter enteritis
Shigellosis
Typhoid fever
Enterotoxigenic Escherichia coli