An outbreak of Shigellosis attributed to consumption of contaminated Well water, Kottamparamba, Calicut, Kerala, India, 2020

  • Water or foodborne
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Background:
In India, over 100,000 people die of water-borne diseases annually. On December 11, 2020, District Surveillance Unit, Calicut, Kerala, notified a cluster of loose stools in Kottamparamba, Calicut. We investigated the outbreak to identify the potential exposures and propose recommendations.

Methods:
We defined a case as loose stools (≥3 episodes) or vomiting in a resident of Kottamparamba, December 2020. We actively searched and line-listed the cases. We described cases by time (epi-curve), place (spot map), and person (attack rate by age and gender). We conducted the environmental investigation, interviewed a key informant and generated a hypothesis. We conducted a case-control study to test the hypothesis. We defined the case as loose stools or vomiting in a resident of Kottamparamba; and controls as a resident of Kottamparamba without symptoms. We computed Odds Ratio (OR) and 95% confidence interval (95%CI) by comparing the attack rates between cases and control. We sent 14 stool specimens and well water for laboratory investigation.

Results:
We identified 53 (33%) cases and 1 death (case-fatality rate= 0.02%) among 161 residents. Attack rate was higher among <15 age group (64%, (25/39) and males (35%, (29/84). Spot map has shown clustering of cases around a well. We identified seepage of sewage water from the subterranean pipeline into the well used for drinking and cooking purposes during the environmental investigation. We recruited 53 cases and 108 controls to test the hypothesis of well-water could be the potential exposure. Cases were more likely to have consumed contaminated water from the well than controls (OR=11.2, 95%CI=3.5-35.7). The water analysis reports and stools samples shown the presence of Shigella Sonnie.

Conclusions:
Contaminated well water due to seepage of sewage led to an outbreak of Shigellosis in Kottamparamba. We recommended repairing the subterranean pipelines and regular chlorination of well water.

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