Which Vibrio cholerae serogroup is linked to epidemic disease due to toxigenic strains?

• A. O1
• B. O2
• C. O3
• D. O4

Answer: (A)

Epidemic cholera is driven by toxigenic strains of Vibrio cholerae that belong to the O1 serogroup. These strains carry the cholera toxin gene (ctxAB) and other virulence factors, enabling them to colonize the small intestine and trigger massive watery diarrhea through toxin-mediated secretion of electrolytes and water. This combination—toxigenic capacity plus a serogroup that spreads widely in populations with contaminated water—explains why O1 is the classic cause of epidemic cholera. Other serogroups listed typically do not drive large epidemics caused by cholera toxin-producing strains, though some non-O1 strains can cause sporadic gastroenteritis. (A second serogroup, O139, has caused outbreaks in some regions, but the question points to the classic epidemic-associated serogroup, which is O1.)