Post-wedding outbreak of profuse watery diarrhea in a hill district
In a hill district, 27 people developed profuse watery diarrhea within 36 hours after attending a wedding feast of 180 guests. Four are severely dehydrated and one elderly woman died at home before reaching hospital. The feast was held in a village where households use water from a spring piped through a broken section lying within two meters of a pit latrine. Most guests ate rice, goat curry, and a raw vegetable salad; a smaller group drank only bottled water. The district hospital has no microbiology laboratory but can send samples to the provincial laboratory, 24 hours away by road. Health workers have already opened an oral rehydration corner. The district health officer asks you to lead the response.
1. State a working case definition and list the immediate outbreak control measures you would institute before laboratory confirmation.
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Case definition: a person aged 5 years or older living in the affected village or who attended the wedding feast, with acute watery diarrhea (three or more loose stools in 24 hours) with onset between 24 hours before and 5 days after the feast; a suspected case is any such person, and a confirmed case is one with Vibrio cholerae isolated from stool. Immediate control: establish a treatment camp with oral rehydration and intravenous fluids for severe dehydration; isolate cases and provide safe water and sanitation; chlorinate the spring and all household water, repair the pipe, and promote handwashing and safe food; conduct active case finding and daily reporting; and ensure safe burial of the deceased. Notify the district and provincial health authorities. Because one death has occurred, do not wait for laboratory confirmation before instituting cholera control. Health education should be practical: boil or chlorinate water, cook food, and use latrines. Monitor daily attack rates to judge whether control is working.
2. Which specimens would you collect and why, given that the provincial laboratory is 24 hours away?
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Collect stool or rectal swabs from at least 10–15 current cases, placed in Cary-Blair transport medium, and send them to the provincial laboratory for culture and sensitivity; if cholera is suspected, request TCBS culture and serotyping. Also collect water samples from the spring, the storage tank, and the broken pipe section, and test for fecal coliforms and Vibrio cholerae. Take food samples if any remain, and interview food handlers. The rationale is to identify the organism, confirm the vehicle, and guide antibiotic choice; a single clinical case is not enough because other pathogens such as rotavirus, enterotoxigenic E. coli, or Shigella can cause similar illness. Blood cultures are not useful in cholera. If laboratory transport is delayed, use rapid dipsticks where available and treat empirically. Document sample times and chain of custody, because the findings may be used for legal and public health action.
3. How would you investigate the vehicle of transmission, and how would you interpret a strong association with one food item?
Read the worked answer
Conduct a retrospective cohort study of all 180 guests. Obtain the guest list, interview by phone or in person, and record exposures: attendance, foods eaten (rice, goat curry, raw salad), water source, bottled water, and handwashing. Record outcome using the case definition and date of onset. Calculate attack rates for exposed and unexposed guests for each exposure, and relative risk with 95% confidence intervals. A food or water item with a high attack rate in the exposed and low in the unexposed, a temporal sequence, and a dose-response pattern supports a vehicle. Interpretation: if illness is strongly associated with the raw salad or with spring water and not with bottled water, that points to contamination during preparation or from the water supply; the broken pipe near the latrine supports fecal contamination. Even a negative laboratory result does not exclude cholera if specimens were collected late. Use the findings to target control and to write a report.