The burden of cholera in the slums of Kolkata - A community based study by NICED

This paper by National Institute of Cholera and Enteric Diseases (NICED) is based on a prospective, community based study in an impoverished urban site in Kolkata in order to measure the burden of cholera, describe its epidemiology, and search for potential risk factors that could be addressed by public health strategies. The study population was enumerated at the beginning and end of the study period. Surveillance through five field outposts and two referral hospitals for acute, watery, non-bloody diarrhoea was conducted from May 2003 to April 2004.

Data and a stool sample for culture of Vibrio cholerae was collected from each patient. Treatment was provided in accordance with national guidelines. From 62329 individuals under surveillance, 3284 diarrhoea episodes were detected, of which 99% had a stool sample collected and 4% were culture confirmed cholera. 15% were children less than 2 years of age, 23% had severe dehydration, and 38% were hospitalised. Risk factors for cholera included a household member with cholera during the period of surveillance, young age, and lower educational level.

The study concludes that -

• The risk factors for cholera, including having a household member with cholera detected during the study period, young age, and lower educational level are not easily amenable to intervention.
• It was also interesting to note that adults with cholera had a lower educational level compared to those with other diarrhoeal illnesses.
• The results also emphasise the high household transmission of cholera. Improvements in living conditions could potentially prevent and ameliorate the effects not only of cholera but of diarrhoeal diseases in general. 
• Implementation of adequate public health infrastructure for the whole population in need may not be possible in the near future. Mass vaccination could be a potentially useful tool to prevent seasonal cholera in the area.
• A large cluster randomised efficacy trial of a killed, whole cell oral cholera vaccine is planned in Kolkata. 
• Herd immunity against cholera would be essential in communities such as this with very crowded living conditions and where household contact is a clear risk factor for disease. 
• There are plans to explore the population rates of other diarrhoeal disease aetiologies in future studies.

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