Update March 28, 2019


primary modes of pathogen transmission

Pathogens such as Vibrio choleraeare water-borne and transmitted via a contaminated water supply. Several pathogens, including S aureus and Bacillus cereus, are transmitted by contaminated food.

Some pathogens, such as Shigella and Rotavirus, are transmitted by person-to-person spread and are, therefore, commonly seen in institutional settings such as child care centers.

Finally, Clostridium difficileinfection can result from overgrowth after antibiotic administration.


What is the likely anatomic site of infection in this case? Why?

B. The description of this patient’s diarrhea as profuse and watery suggests a small bowel site of infection. The small bowel is the site of significant electrolyte and fluid transportation. Disruption of this process leads to the production of profuse watery diarrhea, as seen in this patient.


What is the most likely pathogen in this case? What is the pathogenetic mechanism by which it causes diarrhea?

C. The most likely cause of diarrhea in this patient, who has recently returned from Mexico, is enterotoxigenic E coli (ETEC), which is the most common cause of traveler’s diarrhea.

Diarrhea results from the production of two enterotoxins that “poison” the cells of the small intestine, causing watery diarrhea. ETEC produces both a heat-labile and a heat-stable enterotoxin. The heat-labile enterotoxin activates adenylyl cyclase and the formation of cAMP, which stimulates water and electrolyte secretion by intestinal endothelial cells. The heat-stable toxin produced by ETEC results in guanylyl cyclase activation, also causing watery diarrhea.


Content 4



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