Dengue cluster in a Kratie village: rapid risk assessment
During the third week of July, a health center in a rice-farming village in Kratie reports 48 suspected dengue cases from a population of 1,200. Of these, 30 are NS1-antigen positive, 6 have been hospitalized, and 1 died. The cases are clustered in three hamlets near water storage jars and discarded tires. The health center has 3 staff, no entomologist, and limited larvicide. Schools remain open. The village chief wants to wait for the district team before any community action. A local radio station offers one 15-minute slot. The provincial dengue program asks for a rapid risk assessment and an action plan for the next 7 days. Recent rain has filled containers; 20% of inspected houses have larvae. One hamlet has no piped water.
1. Calculate the attack rate, confirmed attack rate, hospitalized proportion, and case fatality. Interpret the figures with caveats.
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Suspected attack rate = 48/1,200 × 100 = 4.0%. Confirmed attack rate = 30/1,200 × 100 = 2.5%. Hospitalized proportion among suspected cases = 6/48 × 100 = 12.5%. Crude case fatality = 1/48 × 100 = 2.1%; confirmed-case fatality = 1/30 × 100 = 3.3%.
These figures suggest an outbreak with a serious clinical burden. The 20% larval positivity supports local transmission. Caveats: the denominator may include temporary residents; suspected cases may be misclassified; NS1 sensitivity falls after day 5; not all cases may be reported; small numbers make fatality unstable. The figures justify urgent action but should be updated daily as laboratory results and new cases arrive.
2. Prioritize actions for the next 7 days. Should schools close? Justify your choices.
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Priority 1: source reduction. Remove or cover water jars, tires, and containers; apply larvicide where appropriate; organize household cleanup in the three hamlets. Priority 2: case detection and triage. Review fever cases daily, use NS1 testing where available, teach warning signs, and refer early. Priority 3: risk communication through the radio slot and village meetings, covering fever danger signs and container control. Priority 4: coordinate with the district and provincial teams and request vector-control support.
School closure is not the first action. Dengue is vector-borne, not spread person-to-person. Closing schools without source reduction may not help and disrupts education. If a school has many cases or breeding sites, inspect and clean it, and consider targeted closure only if the public health authority advises. The village chief should not wait; simple environmental actions can start immediately.
3. Design a brief evaluation plan with indicators for the 7-day response.
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Indicators: number of houses inspected and percentage with larvae eliminated; number of containers treated or removed; number of fever cases screened and referred; time from case report to investigation; percentage of suspected cases with an NS1 result; number of radio and community sessions and estimated reach; larvicide and ORS stock; staff trained.
Use a simple line list and review daily, with a 7-day summary. Compare larval indices before and after. Document hospitalizations and deaths. Use the data to adjust targeting, not just to report activity. Assign one staff member to maintain the line list and share a brief daily summary with the district team.