An outbreak of acute diarrhoeal disease caused by Shigella sonnei in a village in Dibrugarh district, Assam.

Background & objectives Food and waterborne illnesses remain a neglected public health issue in India. Events with large gatherings frequently witness outbreaks of acute diarrheal diseases due to consumption of contaminated food or water or poor food handling practices. In the present study, an outbreak of acute diarrhoeal disease (ADD) occurring among the attendees of a birthday party in rural Dibrugarh district in the northeastern Indian State of Assam was investigated. Methods Sociodemographic information along with details of ADD outbreak that included information about source of foods, food handlers, illness details, etc., were collected using an outbreak investigation form for descriptive and analytical epidemiology. Rectal swabs from affected individuals and food handlers were collected along with bore-well water samples and tested in the laboratory by performing bacterial culture, biochemical analysis and polymerase chain reaction. Due to the delayed report on the outbreak, collecting leftover food for laboratory testing and analysis was impossible. Results A total of 25 cases of ADD had similar signs and symptoms. The mean incubation period for developing acute diarrhoea was 26.36±8.76 (± standard deviation) hours from food consumption. The overall attack rate was 60.04 per cent (25/41); 20 per cent (5/25) required hospitalization. Thirteen rectal swab samples were tested for pathogens and found positive for Shigella sonnei. Antibiotic susceptibility test of isolated S. sonnei showed resistance to nalidixic acid, ciprofloxacin and cefotaxime. Consumption of one of the food items - chicken curry was significantly associated with illness (Odds Ratio=14.8; 95% Confidence Interval: 2.75-85.11); P value<0.05 and Population Attributable Fraction (PAF) was 70.18 per cent. The water samples were found satisfactory for human consumption. Interpretation & conclusions The findings suggested that S. sonnei infection could be implicated in the investigated food-borne diarrhoeal disease outbreak and that there was a potential for human-poultry cross-infection. Additionally, the study revealed concerning levels of S. sonnei resistance to recommended antibiotics and drew attention to their public health relevance.