Infectious Diarrhea

Overview
  • Infectious agents account for the vast majority of "Acute Diarrhea" cases, defined as a course of diarrhea less than 3 weeks long. It should be pointed out that many of the mechanisms by which microorganisms cause diarrhea could be categorized under the other pathophysiologies of diarrhea; however, we group any infectious cause of diarrhea, regardless of its molecular mechanism, under this heading.
Clinical Approach
  • A comprehensive history, physical, and panel of laboratory results are critical in narrowing the list of possible infectious organisms. Certain foods are often associated with particular infectious agents and thus a list of recently ingested items should be compiled. Constitutional symptoms indicate that the microorganism has invaded into the GI mucosa and thus initiated a systemic immune response. The presence of blood in the diarrheal feces indicates that the microbe has damaged the large or small intestinal mucosa, either by producing cytotoxins or by physically invading the mucosa. Stool cultures are extremely helpful in direct micobiological diagnosis of infectious diarrhea.
Pathophysiology
  • Overview
    • Virulent intestinal microbes can result in diarrhea by the gamut of possible pathophysiological mechanisms. Below we solely discuss some general themes whereas specific molecular mechanisms are described on the pages of the causative organisms.
  • Enhancement of Intestinal Secretion
    • This is usually caused by microbial enterotoxins which induce excessive activation of pathways regulation small intestine secretion or large intestine secretion. Because these microorganisms generally do not invade the GI Mucosa, they typically do not cause fever, constitutional symptoms, or a bloody diarrhea.
  • Impairment of GI Water and Electrolyte Absorption
    • A variety of processes can disrupt intestinal water and electrolyte absorption, thus leading to diarrhea. Microbial adherence to the large or small intestine epithelium generally produces only watery diarrhea because there is no mucosal cell death or invastion. Production of cytotoxins by culprit bacteria may result in blood and presence of inflammatory cells in the stool but no constitutional symptoms since there is no actual invasion of the mucosa. Microbial invasion of the intestinal mucosa will result in blood and inflammatory cells in the stool along with initiation of a systemic immune response which will manifest as constitutional symptoms such as fever.
Etiological Organisms