Figure 3. Clinically apparent dengue in different age groups in Sri Lanka, 2003–2006, Sri Lanka. Because true incidence data were not available, relative incidence of dengue infections by age cohort was estimated. We used Genetech data and known population of Colombo by age, to estimate relative incidence. The age group (>60 years) with the lowest transmission rate was used as a referent for calculating the fold difference between each remaining cohort and the referent.