Question
A 36 years man was having watery diarrhea and vomiting. He was admitted to the hospital for management of dehydration. Answer the following: Define diarrhea. Enumerate the bacterial etiologic agents of diarrhea. Describe the pathogenesis of this clinical entity. How will you provide prophylaxis. (1+2+5+2)
Answer
Definition of diarrhoea: the passage of three or more loose/watery stools in a 24-hour period (or a clear increase in stool frequency/liquidity from the individual’s normal pattern), reflecting an imbalance between intestinal fluid secretion and absorption.
Bacterial etiologic agents of diarrhoea:
- Secretory (non-invasive, toxin-mediated): Vibrio cholerae, Enterotoxigenic E. coli (ETEC), Staphylococcus aureus (food poisoning), Bacillus cereus, Clostridium perfringens.
- Invasive/inflammatory (dysenteric): Shigella species, Enteroinvasive E. coli (EIEC), Enterohaemorrhagic E. coli (EHEC), Campylobacter jejuni, non-typhoidal Salmonella, Yersinia enterocolitica.
- Other: Clostridium difficile (antibiotic-associated).
Pathogenesis Diarrhoea can arise by two broad mechanisms:
- Secretory (non-inflammatory) diarrhoea — the organism does not invade the mucosa but produces an enterotoxin that stimulates active fluid/electrolyte secretion (e.g., cholera toxin activates adenylate cyclase, raising cAMP; ETEC’s heat-labile toxin acts similarly, its heat-stable toxin raises cGMP), overwhelming the gut’s absorptive capacity and producing profuse watery stools without mucosal destruction, blood, or significant faecal leukocytes.
- Invasive (inflammatory) diarrhoea — the organism directly invades and destroys colonic/ileal epithelium (e.g., Shigella, EIEC penetrate and multiply within enterocytes, causing cell death and mucosal ulceration; Campylobacter and non-typhoidal Salmonella similarly invade the mucosa), producing an inflammatory response with faecal leukocytes, and clinically presenting as dysentery (blood, mucus, tenesmus, fever) rather than purely watery stool.
- Regardless of mechanism, the common physiological endpoint is a net imbalance favouring intestinal fluid loss over absorption, leading to dehydration (isotonic in profuse secretory diarrhoea like cholera) and electrolyte derangement, the basis of the clinical severity and the rationale for rehydration therapy.
Prophylaxis Safe drinking water supply and proper sanitation/sewage disposal; food hygiene (thorough cooking, avoiding contaminated food/water); hand hygiene and health education; breastfeeding promotion in infants (protective secretory IgA); vaccination where available (oral cholera vaccine, typhoid vaccine); prompt case management and oral rehydration therapy to reduce severity/transmission during outbreaks; safe disposal of excreta from cases.