Severity: Can be life-threatening; most infections are asymptomatic or mild.
Treatment Outcome: With proper rehydration therapy, mortality rate is less than 1%.
Infectivity and Risk Factors
Transmission Mechanism: Acquired via the fecal-oral route; requires a large infectious dose.
Increased Susceptibility Due to:
Use of proton-pump inhibitors (PPIs) and antihistamines.
Having type 0 blood.
Conditions of poor sanitation and overcrowding.
Prior vagotomy (a surgical procedure that removes part of the vagus nerve).
Helicobacter pylori infection.
History and Physical
Symptom Spectrum: Ranges from asymptomatic to severe, profuse diarrhea.
Common Symptoms:
Diarrhea
Abdominal discomfort
Vomiting
Severe Cholera:
Distinguished by rapid loss of fluid and electrolytes.
Stool Description: “Rice water” consistency, possibly containing bile and mucus.
Fluid Loss Rate: Up to 1 liter/hr in adults, 20 cc/kg/hr in children.
Effects of Hypovolemia:
Dry oral mucosa
Cool skin
Decreased skin turgor
Hyperventilation and Kussmaul breathing due to lactic acidosis.
Electrolyte Imbalances: Hypokalemia and hypocalcemia leading to muscle weakness and cramping.
Acute tubular necrosis
Renal failure
Severe hypotension
Death
Evaluation
Diagnosis Criteria:
Based on clinical suspicion.
High volume diarrhea and history of travel to an endemic area may suffice for diagnosis.
Laboratory Confirmation:
Isolation and culture of V. cholerae from stool.
Culture Enhancement: Use of selective media with high pH.
Rapid Tests: Identification of O1 or O139 antigen in stool using dipsticks or darkfield microscopy.
Treatment / Management
Fluid Resuscitation:
Mild to Moderate Dehydration: Oral rehydration solution (ORS), preferably rice-based to reduce diarrhea duration and stool volume.
Severe Dehydration/Hypovolemic Shock: Intravenous fluids, typically 100 mL/kg of lactated Ringer’s solution within the first three hours.
Outcome Improvement: Prompt fluid treatment can reduce mortality from over 10% to less than 0.5%.
Antibiotic Therapy:
First Line: Tetracyclines (e.g., single 300 mg dose of doxycycline or 500 mg of tetracycline every 6 hours for 2 days).
Resistance Issues: Alternative therapies such as macrolides (erythromycin, azithromycin) or fluoroquinolones (ciprofloxacin) may be necessary.
Epidemiology
Dominant Serogroups:
O1: Majority of cases globally, includes Classical and El Tor variants.
O139 (‘Bengal’): Emerged in 1992, prevalent in South and Southeast Asia.
Major Outbreaks:
2010: Large epidemic in Haiti, spread to Dominican Republic and Cuba, now endemic in Hispaniola.
Ongoing: Persistent large outbreaks in Yemen and sub-Saharan Africa.
Incidence Rates:
Africa: Typical rate of 0.3 per 10,000 in endemic settings; spikes to approx. 20 per 10,000 during epidemics.
Global (2015 WHO Report): 172,454 cases with 1,304 deaths across 42 countries, case-fatality rate 1-5%.
Infants and Young Children (1–4 years): Highest incidence rates, between 1.2 to 8.8 per 1,000.
Risk to Travelers
General Risk: Less than 1:500,000 or 0.001–0.01% per month of stay in a developing country.
Specific Observations:
Japanese Travelers to Bali: Higher incidence rate (13:100,000); potential reasons include intensive surveillance, higher raw seafood consumption, and prevalent atrophic gastritis.
United States (2010-2014):
Reported Cases: 90 cases in travelers, mostly acquired in the Caribbean (75%) and India (10%).
Risk Factors: Cases linked to consumption of high-risk foods like raw/undercooked seafood or untreated water in South America.
Challenges in Surveillance
Active vs. Passive Surveillance: Active surveillance studies often report higher incidences than routine passive systems.
Under-recognition Factors:
Clinical Similarity: Mild cholera cases are hard to distinguish from other types of acute watery diarrhea.
Investigation Limits: Most cases of acute travelers’ diarrhea are not specifically tested.
Cultural Requirements: Specialized culture media needed to grow cholera bacteria.
Impact of Under-recognition: Minimal, since cholera responds well to standard treatments and secondary transmission from travelers is rare.
Composition: Contains heat and formalin-inactivated Inaba, Ogawa, Classic, and El Tor strains of V. cholerae O1 and recombinant cholera toxin B subunit (rCTB).
Manufacturers: CSL Limited and Crucell Sweden AB.
Dosage and Administration:
Adults and Children >6 Years: 2 doses, 1–6 weeks apart. Restart the vaccination if the second dose is delayed beyond 6 weeks.
Children aged 2–6 years should receive 3 doses of vaccine. If an interval of more than 6 weeks occurs between any of the doses, restart the vaccination.
To be taken on an empty stomach (no food or drink 1 h either side of dose) as an oral suspension with an alkaline buffer solution (as per the package instructions)
Vaccine Efficacy
High Initial Protection:
El Tor cholera: 85% protection for 6 months in children and adults, reducing to 62% after 1 year and 57% after 2 years.
Age-Dependent Efficacy:
>5 Years: 78% protection at 1 year, 63% at 2 years.
Children 2–6 Years: 44% at 1 year, dropping to 33% by 2 years.
<5 Years: Protection decreases to zero by 3 years post-immunisation.
Onset of Effectiveness: Effective from 1 week after the second dose.
Limitation: Does not confer immunity to V. cholerae O1 and O139 serogroups; Dukoral is monovalent.
Additional Vaccine Efficacy
Against LT-ETEC:
Reduction in Diarrhea: 60% reduction in LT-ETEC-related diarrhea as a secondary outcome in vaccine trials.
Duration: Protection lasts approximately 3 months.
Booster Requirements
Booster Frequency:
Adults and Children >6 Years: Every 2 years.
Children 2–6 Years: Every 6 months.
Re-Immunization: Required if the interval exceeds 2 years for adults/children over 6 years or 6 months for children 2–6 years.
Adverse Effects
Incidence: Very low, with mild abdominal pain and diarrhea reported in 0.1–1% of recipients.
Severity: Free of significant adverse effects.
Interactions
With Other Vaccines: Can be co-administered without affecting efficacy.
Specific Interactions: Must be administered at least 8 hours apart from Ty21a vaccine.
Recommendations
General Guidance:
No Entry Requirement: No country requires cholera vaccination for entry.
Not Recommended for Routine Travelers: Due to low risk and mild nature of the disease.
Suggested for Specific Groups:
Humanitarian Workers: In epidemic or refugee situations.
Visitors to Relatives: Especially in unsanitary conditions in endemic areas.
Individuals with Pre-existing Conditions: Like inflammatory bowel disease or malabsorption, which could be worsened by cholera.
Travellers with Achlorhydria: Increased risk in endemic areas.
Off-Label Use:
Travelers’ Diarrhea: Considered for those at risk of severe complications, though not officially licensed for this purpose in Australia.
