Distribution of confirmed hospitalized DHF cases at 2 month intervals from 1973 through 2001. There has been general upward trend with larger outbreaks at occuring at 2 – 5 year intervals. Peak hospitalization rates occur during the rainy season month of July – August. Colored graphs show isolations of different dengue viruses demonstrating off-set outbreaks of DENV 3 and 4 compared with DENV 1 – 2.