Ecological study of <e1>Vibrio cholerae</e1> in Vellore

Vellore is endemic for cholera due to <e1>Vibrio cholerae</e1> O1 and O139. In a previous study the prevalence of <e1>Vibrio cholerae</e1> in drinking water, lakes and sewage outfalls in a single 2-months period in Vellore, India was determined. In addition water samples from three sites were also tested for the presence of <e1>V. cholerae</e1> O1 and O139 by fluorescent antibody staining. This follow on study has examined how the environmental distribution of <e1>V. cholerae</e1> at the same sites alters over a 12-month period and the relationship to the clinical pattern of cholera in Vellore. Samples of water were collected from fixed sites at three water bodies each month between April 1997 and March 1998. Bacteria isolated from samples were identified by standard biochemical tests and isolated strains of <e1>V. cholerae</e1> tested for their ability to agglutinate O1 and O139 antisera. Samples were also tested for the presence of <e1>V. cholerae</e1> O1 and O139 by fluorescent antibody staining. The clinical isolation rate of <e1>V. cholerae</e1> in Vellore, maximum temperature and rainfall were also studied. The results demonstrate the presence in the environment of viable but non-cultivable (VNC) <e1>V. cholerae</e1> in 10 of 12 months of the study year as well as their viability. Their prevalence in the environment also correlated with the isolation of these pathogens from clinical samples over the same study period.