Which is the most common serogroup of Vibrio cholerae responsible for epidemic and pandemic cholera worldwide?

Explanation

## Vibrio cholerae Serogroups **Key Point:** The O1 serogroup of *Vibrio cholerae* is the most common cause of epidemic and pandemic cholera. It has been responsible for all seven pandemics since 1817. ### Classification of Vibrio cholerae Serogroups | Serogroup | Toxigenic Potential | Epidemiology | Clinical Significance | |-----------|-------------------|--------------|----------------------| | **O1** | Yes (CTX-positive) | Epidemic and pandemic strains | Most common; all 7 pandemics | | **O139** | Yes (CTX-positive) | Endemic in Bangladesh/India; epidemic potential | Emerged 1992; limited spread | | **O141** | No (CTX-negative) | Rare; sporadic cases | Non-toxigenic; mild disease | | **Non-O1, Non-O139** | No (CTX-negative) | Sporadic; environmental | Cause mild gastroenteritis only | ### O1 Serogroup Characteristics **High-Yield:** The O1 serogroup is divided into two biotypes: - **Classical biotype:** Produces classical cholera toxin; largely replaced by El Tor - **El Tor biotype:** More virulent, produces more toxin, better environmental survival; causes current pandemics **Mnemonic:** **O1 = Outbreak** — O1 is the serogroup that causes outbreaks and pandemics. ### Historical Pandemic Data 1. **1st–6th pandemics (1817–1923):** O1 Classical biotype 2. **7th pandemic (1961–present):** O1 El Tor biotype - Began in Indonesia - Spread to Africa, Americas, Asia - Continues to cause epidemic cholera globally ### Why O1 is Most Common 1. **Toxigenic:** Carries the CTX phage encoding cholera toxin 2. **Epidemic potential:** Causes severe, recognizable disease → epidemiological tracking 3. **Environmental survival:** El Tor biotype survives better in water and food 4. **Pandemic history:** Documented in all seven pandemics 5. **Current prevalence:** Responsible for >99% of reported cholera cases **Clinical Pearl:** O139 emerged in 1992 in Bangladesh and caused a localized epidemic, but it has not achieved the pandemic spread of O1. Non-O1, non-O139 strains are non-toxigenic and cause only mild gastroenteritis, not epidemic cholera. ### O139 Serogroup (Important Distinction) - Emerged in 1992 in Bangladesh - Toxigenic (CTX-positive) - Caused regional epidemic but limited global spread - Lacks the O antigen of O1 but is still virulent - Never achieved pandemic status like O1 [cite:Jawetz, Melnick & Adelberg's Medical Microbiology 28e Ch 21; Park's Textbook of Preventive and Social Medicine 26e Ch 8]