Forty-six cases of watery diarrhoea around one leaking hand pump
On 3 July the subcentre serving three hamlets with a combined population of about 1,200 reports 46 people with acute watery stools over five days, including 12 children under five. Three children were severely dehydrated on arrival and one 3-year-old died at home before reaching the facility. All affected families draw water from a single hand pump that stands 8 metres from an open drain and a row of pit latrines; the pump base leaks and the ground around it is permanently wet. Households store water in wide-mouthed pots covered with cloth. The subcentre has ORS, intravenous fluids and a weighing scale, but its chlorine tablet stock expired in March. A local leader says the water comes from deep down and cannot be dirty, and asks you to give Preventive medicine to everyone instead of worrying about the pump.
1. Calculate the attack rate from these figures and state two additional pieces of information you need before drawing conclusions, explaining why each matters.
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The crude attack rate is 46 cases among 1,200 people, which is 3.8% over five days. The case fatality rate so far is 1 in 46, about 2.2%, which is high enough to demand urgent action and suggests both a virulent organism and delayed care-seeking.
But a crude rate can mislead. First, I need a proper case definition with dates - what counts as a case, from which day - so that I can construct an epidemic curve. A single sharp peak suggests a point-source exposure such as a contaminated water supply, while a continuing plateau suggests person-to-person spread, and the two demand different control measures. Second, I need the attack rate calculated by exposure: among families using the hand pump versus those using any other source, with the same case definition. Comparing these gives a relative risk, and it is this comparison, not the crude 3.8%, that implicates or exonerates the pump. A crude rate of 3.8% would look identical whether or not the pump were involved.
I would also want the age distribution and the number of severely dehydrated cases, since a high proportion of adults with severe watery stools points towards cholera rather than rotavirus, and that changes the urgency of culture and of household chlorination.
2. Rank your first five actions for the next 24 hours and justify the order.
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First, treat. Set up oral rehydration corners in each hamlet, train village volunteers and anganwadi workers to give ORS by spoon, and keep intravenous fluids at the subcentre for severe dehydration. This is first because deaths from diarrhoea occur within hours of onset and no environmental measure works fast enough to save the child in front of you.
Second, interrupt the source. Stop use of the leaking pump if an alternative source can be provided, or repair the casing, seal it, and disinfect the well with calculated chlorine, then verify residual free chlorine and get a water sample for faecal coliform testing. The ongoing wet ground and leaking base mean surface waste can track down the casing, so depth is no protection.
Third, provide safe household water: distribute chlorine tablets or bleaching powder with clear dosing instructions, and demonstrate safe storage in narrow-mouthed covered containers with a ladle, not hands or a cloth cover.
Fourth, active surveillance: house-to-house case search with a daily line list, since passive reporting is already missing deaths.
Fifth, specimens and notification: rectal swabs or stool in Cary-Blair from early severe cases to the district laboratory, and formal notification to the health authorities. Laboratory confirmation guides the response but must never delay rehydration or chlorination.
3. How would you answer the local leader, and what water advice would you give the hamlets?
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I would not argue about whether deep water is clean in principle; I would agree that groundwater is usually safer and then explain why this particular pump is different. The casing is leaking, the ground around it is soaked with drainage from latrines and an open drain, and a wet annulus allows surface contamination to travel down the outside of the pipe into the water. That is consistent with cases clustering among the families who use it. Where possible I would demonstrate rather than assert - a chlorine residual test or a hydrogen sulphide vial showing contamination is far more persuasive than a lecture.
On medicines, I would be clear: antibiotics do not prevent cholera and mass chemoprophylaxis is not recommended, because it does not stop transmission, it causes resistance, and it creates a false sense of safety while people keep drinking contaminated water. Giving everyone tablets would also divert the stock needed for the severely ill.
Household advice: boil water for one minute, or chlorinate with the correct dose and let it stand 30 minutes; store in a narrow-mouthed covered pot; take water out with a long-handled ladle and never with hands or a cup that has touched the mouth; and wash hands with soap after defecation and before food. Also, anyone with watery stools should start ORS immediately and come to the subcentre if there is vomiting, sunken eyes or no urine.