Infectious Disease · Gastrointestinal Infections
The facts most likely to be tested
Vibrio cholerae is a comma-shaped, gram-negative, oxidase-positive rod transmitted via contaminated water or shellfish.
The pathogenesis involves the cholera toxin, which constitutively activates adenylate cyclase to increase cyclic AMP (cAMP) levels in intestinal epithelial cells.
Patients present with profuse, painless, watery diarrhea classically described as rice-water stools.
Severe cases lead to rapid dehydration, hypovolemic shock, and metabolic acidosis due to massive loss of bicarbonate in the stool.
The primary and most critical intervention for management is aggressive oral rehydration therapy (ORT) with electrolyte solutions.
Antibiotics such as doxycycline or azithromycin are used as adjuncts to reduce the duration of symptoms and volume of stool output.
Diagnosis is confirmed via stool culture on thiosulfate-citrate-bile salts-sucrose (TCBS) agar, which yields yellow colonies.
Vignette unlocked
A 34-year-old male presents to the emergency department after returning from a relief mission in a disaster-stricken area. He reports 24 hours of frequent, voluminous, painless diarrhea that looks like cloudy water with flecks of mucus. On physical exam, he has sunken eyes, poor skin turgor, and dry mucous membranes. His blood pressure is 88/50 mmHg and his heart rate is 124 bpm. Laboratory studies reveal a bicarbonate level of 14 mEq/L and an elevated creatinine.
What is the most appropriate initial management for this patient?
Aggressive intravenous fluid resuscitation with isotonic crystalloids
This patient presents with severe dehydration and hypovolemic shock secondary to cholera; while ORT is used for mild cases, patients with hemodynamic instability require immediate IV fluid resuscitation to restore perfusion.
Full handout
High yield triage
Etiology / Epidemiology
Caused by Vibrio cholerae via contaminated water/seafood in endemic areas (e.g., post-disaster, poor sanitation).
Clinical Manifestations
Presents with rice-water stools leading to rapid, severe dehydration and hypovolemic shock.
Diagnosis
Stool culture on thiosulfate-citrate-bile salts-sucrose (TCBS) agar is the gold standard.
Treatment
Oral rehydration therapy (ORT) is first-line; Doxycycline is the antibiotic of choice for adults.
Prognosis
Untreated mortality is >50%; with prompt fluid resuscitation, mortality is <1%.
Full handout
Epidemiology & Etiology
Infection follows ingestion of water or food contaminated with Vibrio cholerae, a gram-negative, comma-shaped bacterium. It is highly endemic in regions with poor sanitation and limited access to clean water. Outbreaks frequently occur following natural disasters or in refugee settings.
Pertinent Anatomy
The pathogen colonizes the small intestine, specifically the proximal jejunum. It does not invade the mucosa, but its toxin acts locally on the intestinal epithelium to induce massive fluid secretion.
Pathophysiology
The cholera toxin activates adenylate cyclase, leading to increased intracellular cAMP. This triggers massive secretion of chloride and water into the intestinal lumen, overwhelming the absorptive capacity of the colon. The result is isotonic fluid loss, leading to rapid hypovolemic shock and metabolic acidosis.
Clinical Manifestations
Patients present with sudden onset of voluminous, painless, watery diarrhea described as rice-water stools. Signs of severe dehydration include sunken eyes, poor skin turgor, and absent pulses. If untreated, patients progress to hypovolemic shock and death within hours.
Diagnosis
Diagnosis is confirmed via stool culture on TCBS agar, which shows yellow colonies due to sucrose fermentation. Rapid diagnostic tests are available, but clinical diagnosis is often sufficient in outbreak settings. Monitor serum electrolytes to assess the severity of metabolic acidosis and hypokalemia.
Treatment
The cornerstone of therapy is aggressive fluid resuscitation, primarily via oral rehydration therapy (ORT). Antibiotics are adjunctive to reduce the duration of symptoms and shedding; Doxycycline is the first-line agent for adults. Avoid fluoroquinolones in areas with high resistance. Pediatric patients should receive Azithromycin.
Prognosis
Without intervention, hypovolemic shock leads to death in hours. With aggressive fluid replacement, the prognosis is excellent. Patients must be monitored for hypokalemia and cardiac arrhythmias during the rehydration phase.
Differential Diagnosis
Enterotoxigenic E. coli: milder, self-limiting diarrhea
Rotavirus: common in children, usually associated with vomiting
Shigellosis: presents with bloody stools and fever
Salmonellosis: associated with fever and abdominal pain
Giardiasis: chronic, greasy, foul-smelling stools