Forty-One Cases of Watery Diarrhoea in a Village of 4,200: Whether and How to Notify
A sub-district hospital in a drought-prone block admits 14 patients with profuse watery diarrhoea over two days. By the tenth day the block surveillance register shows 41 cases and 3 deaths, all from one village of about 4,200 people served by four hand pumps. One pump stands about 12 metres from an open drain; a wedding feast for 300 guests was held in the village nine days ago. The medical officer has notified nothing so far, arguing that 'cholera is not confirmed yet' and that the district team is busy with a dengue drive. The expected number of diarrhoea cases in this block for this period, based on the last three years, is about six. The district surveillance officer's office is 62 km away and reachable by telephone. Two of the three deaths occurred in elderly women brought to the hospital only after 36 hours of diarrhoea.
1. Does this situation meet the case definition of an outbreak, and what exactly should the medical officer do about notification, through which channel and within what time?
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Yes. An outbreak is the occurrence of more cases of a disease than expected in a defined area or among a defined group over a given period. Here 41 cases against an expected six is roughly a sevenfold excess; the cases are clustered by place (one village), by time (ten days) and by person (all residents), and the case fatality is 3/41, about 7%. That is an outbreak on epidemiology alone.
Cholera does not need laboratory confirmation to be notified. Under the Integrated Disease Surveillance Programme, a case can be reported as a suspected case; the surveillance system is designed to act on clinical and epidemiological suspicion precisely because culture takes days. Waiting for confirmation defeats the purpose.
The medical officer should telephone the District Surveillance Officer immediately - ideally within 24 hours of recognising the cluster - and simultaneously inform the block chief medical officer. The call is followed by the written outbreak report (the prescribed reporting form for outbreaks, with line list, dates, place, person and deaths) and by routine weekly reporting of the cases already seen. The 'dengue drive' is not a valid reason to defer: the district team's workload does not transfer the legal and ethical duty to report upward.
2. List the immediate control measures, in priority order, and say what specimens should be collected and from whom.
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Priority 1 - prevent deaths. Set up oral rehydration corners at the hospital, the sub-centre and the village; stock ORS and intravenous Ringer's lactate; designate a triage point with a cholera treatment area and strict infection control. Deaths here followed 36 hours of untreated diarrhoea, so the gap was access, not knowledge.
Priority 2 - stop the source. Test residual chlorine in all four hand pumps, shock-chlorinate or close the pump nearest the drain, and advise boiling or halogenation of drinking water. Repair or seal the pump apron and divert the drain. Post health education on hand hygiene and food safety.
Priority 3 - find the cases you have not seen. Active house-to-house case search, a line list with age, sex, date of onset, water source and feast attendance, and daily follow-up of contacts.
Specimens: stool or rectal swabs from about 5–10 of the earliest and currently acute cases (not from convalescent patients), transported in Cary-Blair medium; water samples from each pump for bacteriological analysis and chlorine estimation; and vomit or food remnants if any remain from the feast. Blood cultures only for patients with fever and systemic illness.
3. The wedding feast and the contaminated hand pump are both plausible sources. How should the medical officer tell them apart, and what would each hypothesis predict?
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Compare attack rates by exposure rather than by plausibility.
• Water-source hypothesis predicts: cases distributed according to which pump each household uses; attack rate higher among households served by the pump near the drain; cases among people who never attended the feast; multiple cases within the same household; a rise beginning one to three days after a contamination event (the typical incubation for cholera is a few hours to about five days, commonly one to three) with continuing cases as long as the pump remains contaminated.
• Feast hypothesis predicts: cases overwhelmingly among the 300 guests and their immediate household contacts, with guests from other villages also affected; attack rate linked to particular dishes or to a single food handler; and a sharp peak within the incubation window of the feast. Nine days have now passed since the feast, so a feast-only source should be largely over; continuing incident cases point to an ongoing exposure such as water or person-to-person spread within households.
The discriminating data are the line list exposures, a village map by pump, and guest lists. Note also that the two sources are not mutually exclusive - a feast can amplify an outbreak whose origin is the water supply, and the index case may have contaminated food. The investigation should therefore treat both as candidates until the attack-rate comparison is complete.