Diarrhoeal outbreak in a flood-affected hamlet
You are the community health nurse at a sub-centre covering a village of 3,400 people in a flood-prone district. Over 72 hours, 38 people from the 420 households in the low-lying hamlet have come to your weekly clinic with acute watery stools; nine had severe dehydration, two children aged 3 and 5 years died at home, and four more are being brought in now. The hamlet's tube well is 9 metres from a pit latrine that overflowed during flooding. The sub-centre stocks oral rehydration salts, zinc tablets, 20 kg of bleaching powder, one oral rehydration corner and one rapid test kit for cholera. The primary health centre medical officer is 18 km away and the road is partly flooded; the only ambulance is busy. You have one ANM, one ASHA and three village volunteers. The village head says, 'It is just monsoon diarrhoea, no need to inform anyone.'
1. How do you decide whether this is an outbreak, and what would you do in the next six hours?
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Is it an outbreak? An outbreak is the occurrence of cases in excess of what is normally expected in a defined community over a defined period. Thirty-eight cases in 72 hours among roughly 2,100 people in 420 households, with two deaths and nine cases of severe dehydration, is far above the baseline for a hamlet of that size, and all cases cluster around one water source. That is an outbreak by definition; laboratory confirmation is not the criterion for declaring one.
Next six hours
- Notify the PHC medical officer immediately, and ensure the district surveillance unit receives the report in the prescribed format - this is a reportable event, and the village head's opinion does not override it.
- Open the oral rehydration corner; start low-osmolarity ORS with zinc for 14 days to every case; triage for severe dehydration and arrange urgent transport to the PHC for intravenous fluids.
- Collect stool samples from 5–10 acute cases using the rapid test kit before any antibiotic, and collect water samples from the tube well and stored household water.
- Chlorinate the water source with bleaching powder, advise boiling and safe storage, and stop use of the contaminated source.
- Start a line list - name, age, sex, village, date of onset, symptoms, treatment, outcome - and begin house-to-house case finding with ASHA and volunteers.
- Risk communication on handwashing and safe water, and safe disposal of the overflowing latrine.
2. The medical officer asks you to wait for laboratory confirmation before starting control measures. How do you respond, and what do you document?
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Response
- Explain, respectfully and specifically, that waiting converts a controllable outbreak into a fatal one: in acute watery diarrhoea the deaths occur within hours of onset, and control measures - safe water, chlorination, ORS, case finding - do not depend on identifying the organism.
- Clarify the purpose of the samples: they identify the organism and its antibiotic sensitivity and provide confirmation for surveillance, but they are not a precondition for action.
- Request the medical officer to inform the district surveillance officer and ask for ORS, intravenous fluids and chlorine stock.
- If the advice is to delay reporting, escalate in writing that same day to the district health officer or chief medical officer, copying the medical officer, stating that a reportable outbreak with two deaths is being withheld.
Document (with times)
- The case count, deaths, case definition and date of first case.
- Each telephone call: who was spoken to, what was advised, and the time.
- Samples taken, their identifiers, and where they were sent.
- Actions already started, so no one can claim you did nothing while waiting. Protect patient identity in all reports and never discuss cases with non-authorised people.
3. Design a quick investigation that can identify the source within 48 hours and guide control.
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Step 1 - Case definition and case finding (Day 1) Define a case as three or more loose stools in 24 hours in a resident of the hamlet since the flood, with onset after a fixed date. Do house-to-house active search with the ASHA and volunteers to find unreported cases and deaths.
Step 2 - Descriptive epidemiology Build a line list, plot cases by date of onset (a single sharp peak suggests a common point source, a rising curve suggests continuing exposure or person-to-person spread), compute attack rates by age group, sex and household, and mark cases on a spot map against the tube well and latrine.
Step 3 - Analytic study within 48 hours With 38 cases, a retrospective cohort or a case–control study with two controls per case drawn from the same hamlet, matched for age group, is feasible. Interview about water source, storage vessel, time spent near the overflowed latrine, handwashing, and any common meal or festival. Calculate the attack rate in exposed and unexposed groups and the odds ratio for each exposure.
Step 4 - Environmental sampling Test residual chlorine, and take water samples from the tube well, storage pots and the latrine-contaminated area for faecal coliforms and cholera.
Step 5 - Act on findings - chlorinate, repair or relocate the source, continue ORS and zinc, and re-check attack rates weekly to judge whether control is working.