Classic toxigenic strains of which Vibrio cholerae serogroup are implicated in epidemic infections of Vibrio cholerae?

• A. O1
• B. O2
• C. O3
• D. O4

Answer: (A)

Epidemic cholera is driven by toxigenic strains of Vibrio cholerae that belong to a specific serogroup. The serogroup responsible for classic epidemic cholera is O1. These O1 strains carry the cholera toxin gene, typically on the CTX phage, and their toxin production leads to the severe watery diarrhea that defines cholera outbreaks. Within O1, both the classical and the El Tor biotypes are capable of causing large epidemics, which is why O1 is recognized as the epidemic-causing serogroup. Although another serogroup, O139, can cause outbreaks, it is not the traditional epidemic serogroup, and non-O1/non-O139 strains generally do not drive large epidemics.