In the aftermath of a severe cyclonic storm on 7 January 2012, a
cluster of acute diarrhoea cases was reported from two localities in
Pondicherry, Southern India. We investigated the outbreak to identify
causes and recommend control measures. We defined a case as occurrence
of diarrhoea of more than three loose stools per day with or without
vomiting in a resident of affected areas during 6-18 January 2012. We
used active (door-to-door survey) and stimulated passive (healthy
facility-based) surveillance to identify cases. We described the
outbreak by time, place, and person. We compared the case-patients with
up to three controls without any apparent signs and symptoms of
diarrhoea and matched for age, gender, and neighbourhood. We calculated
matched odds ratio (MOR), 95% confidence intervals (CI), and population
attributable fractions (PAF). We collected rectal swabs and water
samples for laboratory diagnosis and tested water samples for
microbiological quality. We identified 921 cases and one death among
8,367 residents (attack rate: 11%, case-fatality: 0.1%). The attack
rate was the highest among persons of 50 years and above (14%) and
females (12%). The outbreak started on 6 January and peaked on the 9th
and lasted till 14 January. Cases were clustered around two major
leakages in water supply system. Nine of the 16 stool samples yielded
V. cholerae O1 Ogawa. We identified that consumption of water from
the public distribution system (MOR=37, 95% CI 4.9-285, PAF: 97%),
drinking unboiled water (MOR=35, 95% CI 4.5-269, PAF: 97%), and a
common latrine used by two or more households (MOR=2.7, 95% CI 1.3-5.6)
were independently associated with cholera. Epidemiological evidence
suggested that this outbreak was due to ingestion of water contaminated
by drainage following rains during cyclone. We recommended repair of
the water supply lines, cleaning-up of the drains, handwashing, and
drinking of boiled water