Cholera outbreak investigation, Bhadola, Delhi, India, April–May 2018

Background In the Gangetic plains of India, including Delhi, cholera is endemic. On 10 May 2018, staff at the north Delhi district surveillance unit identified a laboratory-confirmed cholera outbreak when five people tested positive for Vibrio cholerae O1 Ogawa serotype in Bhadola. We investigated to identify risk factors and recommend prevention measures. Methods We defined a case as ≥3 loose stools within 24 h in a Bhadola resident during 1 April–29 May 2018. We searched for cases house-to-house. In a 1 : 1 unmatched case control study, a control was defined as an absence of loose stools in a Bhadola resident during 1 April–29 May 2018. We selected cases and controls randomly. We tested stool samples for Vibrio cholerae by culture. We tested drinking water for fecal contamination. Using multivariable logistic regression we calculated adjusted ORs (aORs) with 95% CIs. Results We identified 129 cases; the median age was 14.5 y, 52% were females, 27% were hospitalized and there were no deaths. Symptoms were abdominal pain (54%), vomiting (44%) and fever (29%). Among 90 cases and controls, the odds of illness were higher for drinking untreated municipal water (aOR=2.3; 95% CI 1.0 to 6.2) and not knowing about diarrhea transmission (aOR=4.9; 95% CI 1.0 to 21.1). Of 12 stool samples, 6 (50%) tested positive for Vibrio cholerae O1 Ogawa serotype. Of 15 water samples, 8 (53%) showed growth of fecal coliforms. Conclusions This laboratory-confirmed cholera outbreak associated with drinking untreated municipal water and lack of knowledge of diarrhea transmission triggered public health action in Bhadola, Delhi.