Dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) occur in more than 100 countries and territories. The disease is endemic in Africa, the Americas, Eastern Mediterranean, and most prominent in South East Asia and the Western Pacific. In the last 25 years, the number of countries with DHF has increased more than fourfold. In 1998, 1.2 million cases of dengue and DHF were reported to WHO, accounting for 15,000 deaths.
The number of reported cases is believed to represent only a very small percentage of the global disease, which by some accounts may top 51 million infections each year and has the potential to impact two fifths of the world's population.
Dengue hemorrhagic fever causes death in more than 20 percent of cases of the disease when medical attention is unavailable. That percentage can be reduced to less than 1 percent, however, with modern medical intervention. The same mosquito that carries the yellow fever virus can carry the dengue virus as well. The global rise in urban populations is bringing large numbers of people into contact with infected mosquitoes.