Vibrio cholerae strains. Two serogroups of V. cholerae – O1 and O139 – cause outbreaks. V. cholerae O1 causes the majority of outbreaks, while O139 – first identified in Bangladesh in 1992 – is confined to South-East Asia. Non-O1 and non-O139 V. cholerae can cause mild diarrhoea but do not generate epidemics.