Halophilic gram-negative rods causing massive secretory diarrhea (cholera) or fulminant wound/septic infection (V. vulnificus) after seawater or shellfish exposure.
Also known as: cholera, Vibrio cholerae, Vibrio vulnificus, Vibrio parahaemolyticus, seafood poisoning
Overview
Infections caused by gram-negative, curved (comma-shaped) Vibrio species. V. cholerae produces an enterotoxin causing voluminous watery diarrhea. V. parahaemolyticus causes self-limited gastroenteritis after raw shellfish ingestion. V. vulnificus causes necrotizing wound infections and primary septicemia, especially in patients with chronic liver disease.
Epidemiology
Cholera is endemic in parts of Africa, South Asia, and Haiti, with seasonal outbreaks driven by contaminated water. V. parahaemolyticus is the leading cause of seafood-associated bacterial gastroenteritis in the US. V. vulnificus is most common along the Gulf Coast and during warm months; mortality exceeds 50% in patients with cirrhosis or hemochromatosis.
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Question 1Infectious DiseaseEasy
A 34-year-old missionary returns from rural Bangladesh with 18 hours of profuse, painless, watery diarrhea described as 'rice-water' stools and several episodes of non-bilious vomiting. She reports drinking local well water at a wedding. On exam she is tachycardic to 118, hypotensive at 88/54, with dry mucous membranes, sunken eyes, and decreased skin turgor. Stool dark-field microscopy shows darting, comma-shaped motile rods. Which of the following is the most appropriate first-line management?
AOutpatient observation with oral clear liquids
BLoperamide with bismuth subsalicylate
CAggressive rehydration plus oral doxycycline
DEmpiric metronidazole with bowel rest
Reveal answer & full explanation
Correct answer: C — Aggressive rehydration plus oral doxycycline
AOutpatient observation with oral clear liquids
BLoperamide with bismuth subsalicylate
CAggressive rehydration plus oral doxycycline✓
DEmpiric metronidazole with bowel rest
Why Aggressive rehydration plus oral doxycycline is correct
This patient has cholera caused by Vibrio cholerae, supported by recent travel to an endemic region, contaminated water exposure, voluminous rice-water diarrhea, hypovolemic shock, and characteristic darting comma-shaped organisms on dark-field microscopy
The cornerstone of management is rapid, aggressive volume and electrolyte replacement: oral rehydration solution for mild-to-moderate dehydration and IV lactated Ringer's for severe dehydration or shock, with losses sometimes exceeding 10 L/day
Adjunctive antibiotics shorten illness, decrease stool volume, and reduce shedding; a single oral dose of doxycycline is the WHO-recommended first-line agent in adults (azithromycin in pregnancy and children)
Why the others are wrong
Outpatient observation with oral clear liquids — inappropriate given hemodynamic instability; untreated severe cholera carries mortality up to 50%, falling below 1% with prompt rehydration (premature closure)
Loperamide with bismuth subsalicylate — antimotility agents do not address the secretory toxin-driven fluid loss and may prolong toxin exposure (right-concept-wrong-mechanism)
Empiric metronidazole with bowel rest — metronidazole covers anaerobes and protozoa such as Giardia and amebiasis, not Vibrio (confused-with protozoal diarrhea)
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Ingestion of contaminated water or undercooked shellfish (oysters in particular)
Travel to cholera-endemic regions or refugee settings
Saltwater or brackish water exposure with broken skin (V. vulnificus wound infection)
Chronic liver disease, hemochromatosis, immunocompromise — V. vulnificus septicemia
Achlorhydria or PPI use
Pathophysiology
V. cholerae colonizes the small intestine and secretes cholera toxin, which ADP-ribosylates the Gs alpha subunit → constitutive adenylyl cyclase activation → massive chloride and water secretion into the gut lumen with little inflammation, producing isotonic 'rice water' stools. V. vulnificus expresses a polysaccharide capsule and iron-scavenging siderophores; iron overload states accelerate growth, producing rapidly progressive bacteremia and hemorrhagic bullous cellulitis. V. parahaemolyticus produces a thermostable direct hemolysin causing inflammatory diarrhea.
Clinical presentation
Symptoms
Cholera: sudden painless watery diarrhea progressing to 'rice water' stools, up to 1 L/h, with vomiting and rapid dehydration
V. parahaemolyticus: watery diarrhea, abdominal cramps, low-grade fever 24 h after raw oyster ingestion
V. vulnificus gastroenteritis: severe diarrhea after raw oyster ingestion, especially in cirrhotics
V. vulnificus wound or sepsis: rapidly expanding cellulitis with hemorrhagic bullae, fever, hypotension within hours of seawater exposure
Washerwoman hands (skin wrinkling from severe dehydration)
Hemorrhagic bullae and necrotic skin in V. vulnificus septicemia
Cool, mottled extremities and septic shock
Classic findings
Rice-water stools (cholera) and hemorrhagic bullae with septic shock in a cirrhotic patient after raw oysters (V. vulnificus).
Differential diagnosis
Enterotoxigenic E. coli (ETEC) — Travelers' diarrhea, also watery and toxin-mediated, but less voluminous than cholera
Norovirus — Vomiting predominant, brief duration, outbreaks on cruise ships and in institutions
Necrotizing fasciitis (Group A strep, polymicrobial) — Rapid progression and disproportionate pain, but lacks the saltwater exposure and hemorrhagic bullae characteristic of V. vulnificus
Aeromonas wound infection — Freshwater exposure rather than salt; similar clinical picture, doxycycline still active
Ciguatera or scombroid poisoning — Neurologic or histamine-like symptoms after reef fish ingestion, not diarrhea-predominant
Diagnostic workup
Diagnostic criteria
Clinical picture plus positive culture (TCBS for stool, blood/wound for invasive disease).
Labs
Stool culture on selective TCBS agar (yellow colonies = V. cholerae; green = V. parahaemolyticus, V. vulnificus)
BMP for electrolytes; metabolic acidosis from bicarbonate loss is classic in cholera
Blood cultures in suspected V. vulnificus sepsis
Wound cultures from bullae or debridement specimens
CBC: leukocytosis or leukopenia in V. vulnificus sepsis
Imaging
Not routinely required
CT or MRI for soft tissue involvement to evaluate fascia and abscess
Treatment
First-line
Cholera: aggressive oral rehydration solution (ORS) per WHO formula — backbone of therapy; IV Ringer's lactate if severe dehydration
Cholera antibiotics shorten illness and reduce transmission: doxycycline single dose (adults), azithromycin (pregnancy, children), or ciprofloxacin
V. parahaemolyticus: supportive care; antibiotics only if severe or prolonged
V. vulnificus: doxycycline PLUS a third-generation cephalosporin (ceftriaxone or cefotaxime) — the standard double-coverage regimen
Surgical: aggressive and early debridement for V. vulnificus wound infections
V. cholerae
WHO ORS until losses stop; IV LR for grade III dehydration
Doxycycline 300 mg PO once (adult)
Azithromycin 1 g PO once if pregnant or pediatric
V. vulnificus (wound or sepsis)
Doxycycline + ceftriaxone (or cefotaxime); alternative fluoroquinolone monotherapy in adults
Aggressive surgical debridement
ICU-level resuscitation
Second-line / adjunct
Oral cholera vaccines (Vaxchora, Dukoral) for travelers to endemic regions
Public health reporting required
Complications
Hypovolemic shock and death within hours (cholera)
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