Vibrio cholerae O139
We report results of surveillance for cholera caused by Vibrio cholerae O139 from September 1992, when it was first identified, to December 1998. V. cholerae O139 dominated as the causative agent of cholera in Calcutta during 1992-93 and 1996-97, while the O1 strains dominated during the rest of the period. Dramatic shifts in patterns of resistance to cotrimoxazole, neomycin, and streptomycin were observed. Molecular epidemiologic studies showed clonal diversity among the O139 strains and continuous emergence of new epidemic clones, reflected by changes in the structure, organization, and location of the CTX prophages in the V. cholerae O139 chromosome.

Vibrio cholerae, the gram-negative organism that causes cholera, is well defined on the basis of biochemical tests and DNA homology studies, but the serogroups of the species differ in their pathogenic potential. Of the 193 recognized "O" serogroups of V. cholerae, only O1 and O139 cause epidemic and pandemic cholera. V. cholerae O139 was first identified in September 1992 in southern India and rapidly spread to all cholera-endemic areas in India and neighboring countries. In February 1994, a new clone of V. cholerae O1 El Tor biotype replaced the O139 serogroup as the dominant serogroup causing cholera in Calcutta. After a 33-month quiescent period, a new clone of V. cholerae O139 appeared in August 1996 in Calcutta and was the dominant serogroup until September 1997. This new clone has also spread to other parts of India.

The National Institute of Cholera and Enteric Diseases, Calcutta, conducts continuous surveillance for cholera in Calcutta in particular, and in India in general. During September-October 1998, we observed an increase in the incidence of O139 cholera, prompting study of these O139 strains. We report the findings of surveillance performed from September 1992 to December 1998 in India, which enabled us to track and catalog changes in the O139 strains since its identification.