Most cholera outbreaks are due to faecal contaminated drinking water. On 25 April 2015, Gulbarga district of Karnataka reported 82 diarrhoea cases in Biral B village. We conducted an investigation to identify risk factors for illness and to provide recommendations to control the outbreak and prevent future illness. Methods & Materials: We defined a suspect case of cholera as ≥3 loose stools in 24 hours in a resident of Biral B village between 19 April and 7 May, 2015. We identified cases by

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... ve surveillance through a house to house survey. We conducted a retrospective cohort study in every third household. We interviewed 565 persons in 177 households to assess illness status, socio-demographic characteristics, and potential risk factors including water sources and water treatment. We calculated relative risk (RR) and 95% confidence interval (CI). We collected five stools samples for testing of Vibrio cholerae at district referral laboratory. We assessed water sources, water distribution and tested all sources for faecal coliforms. Results: We identified 169 cases among 2495 villagers (attack rate = 7%). Three fourths (126) were hospitalized with no deaths. Illness onset dates ranged from 22 April to 7 May 2015. The median age was 25 years (range 1-85yrs) with the highest attack rate of 14% (33/235) among 26 to 35 years group and the lowest attack rate of 1.4% (8/561) among the age group 46 to 55 years. The attack rate was 16% (14/86) among persons using water from an unprotected, hand-dug well A for drinking or cooking (RR: 2.2, 95% CI: 1.2-3.8) compared to 10% (15/149) for a second unprotected hand-dug well B(RR: 0.8, 95% CI: 0.5-1.5) and 7% (28/380) for any of six tube-wells (RR: 0.6, 95% CI: 0.4-1.0). One of five stools samples was positive for Vibrio cholerae El Tor Ogawa by culture. Water samples from wells A and B, the six tube wells, overhead tank, and household taps had faecal coliforms and deemed not potable. Conclusion: This suspected cholera outbreak was from using non-potable water particularly from one unprotected well A for drinking or cooking. We recommend chlorination, protection, and regular testing of water sources, particularly well A. http://dx.