Field Investigation of an Acute Diarrhoeal Disease Outbreak in Sabzi Mandi, Urban Ludhiana, Punjab, India, June 2018

Abstract

Background: Acute diarrhoeal disease remains an important public-health problem, particularly where drinking-water systems are vulnerable to faecal contamination. In June 2018, an increase in cases of loose stools was reported from the Sabzi Mandi area of urban Ludhiana, Punjab. Objectives: To confirm and characterize the outbreak by time, place and person; identify potential risk factors and source of transmission; and recommend immediate and long-term control measures. Methods: A suspected case was defined as three or more loose stools within 24 hours in a resident of Geeta Colony, Bharti Colony or Aman Nagar during 3-30 June 2018. Active house-to-house and passive case searches were undertaken. A neighbourhood-matched 1:1 case-control study involving 35 cases and 35 controls was conducted. Stool specimens were tested for Vibrio cholerae, Salmonella and Shigella. Drinking-water samples were assessed for coliforms, faecal coliforms and residual chlorine. The water-distribution and sewerage systems were inspected. Results: Seventy-nine cases were identified among an estimated population of 7,500 (attack rate 10.5 per 1,000); 43 (54.4%) were female and the median age was 16 years (range 7 months-62 years). The highest age-specific attack rate occurred among children aged 0-5 years (55.2 per 1,000). Twenty-seven patients (34.2%) were hospitalized and two deaths were reported (case-fatality proportion 2.5%). No individual exposure in the matched case-control study reached statistical significance. All four stool samples were negative for V. cholerae, Salmonella and Shigella; however, sample transport was delayed. On 4 July, seven of eight water samples showed coliform/faecal-coliform contamination and residual chlorine was absent in all eight. One of two interconnected submersible pumps lacked a chlorine-dosing system; sewer overflow and a drinking-water pipeline leak were also documented. Conclusion: The outbreak was most consistent with faecal contamination of the piped drinking-water system. Environmental and water-quality findings were stronger than the household-level analytic findings. Rapid chlorination, repair of leaks, continued surveillance, safe-water messaging and routine water-quality monitoring were recommended.

Keywords: acute diarrhoeal disease; outbreak investigation; drinking-water contamination; faecal coliform; matched case-control study; Ludhiana; India