Priority setting for vector control
The decision about where to direct search-and-destroy activities for mosquito breeding sites rests on a core epidemiologic distinction:
incidence reflects the rate of new infection in a population, while
case fatality rate (CFR) reflects severity among those already infected. Because breeding-site control is a preventive intervention aimed at interrupting transmission, the barangay with the higher incidence should receive priority.
Incidence is calculated as the number of new cases divided by the population at risk, multiplied by 1,000. For Barangay R, the incidence is
30 ÷ 12,000 × 1,000 = 2.5 per 1,000. For Barangay S, it is
18 ÷ 4,000 × 1,000 = 4.5 per 1,000. Although Barangay R recorded more cases in absolute terms, its larger population dilutes the rate. Barangay S has a smaller denominator, so the same number of cases would represent a much higher risk, and here even a lower case count still yields a higher incidence.
The case fatality rate tells a different story. Barangay R's CFR is
2 ÷ 30 × 100 = 6.7%, while Barangay S has
0%.
CFR measures how lethal the disease is among diagnosed cases, not how widely it is spreading in the community. A high CFR signals problems in early recognition, timely consultation, or clinical management, and it should trigger review of those services rather than redirect vector control resources.
| Measure | What it answers | Barangay R | Barangay S | Implication for priority |
|---|
| Incidence per 1,000 | How fast is infection spreading? | 2.5 | 4.5 | Higher in S, so S gets vector control priority |
| Case fatality rate | How severe is the disease among cases? | 6.7% | 0% | Higher in R, but this guides case management review, not breeding-site control |
Watch out! Do not equate a larger number of cases with a larger public health threat. The denominator matters. A small barangay with few cases can have a much higher incidence than a large barangay with many cases.
Key point! Vector control targets the risk of new infection, so the metric that drives prioritization is incidence. Fatality data are used to evaluate the quality of clinical care and health-seeking behavior, not to decide where to destroy mosquito breeding sites.
The broader literature supports this framing. Dengue transmission is driven by the interaction of the
Aedes aegypti vector with environmental conditions such as temperature, humidity, and urbanization, and vector competence is shaped by genetic and ecological factors . Spatial analyses of dengue incidence consistently use incidence rates, not raw case counts or fatality rates, to identify high-risk clusters and guide targeted interventions . When public health agencies set priorities for vector-borne disease control, they weigh criteria that include transmission risk and intervention effectiveness, which aligns with using incidence as the primary indicator for preventive vector control .