00000000Confirmed as dengue. Thus, in a period of six years, Mexico evolved from having no reported dengue to having epidemics every year, three endemic virus serotypes and sporadic occurrence of haemorrhagic disease. Currently, epidemic dengue is one of Mexico's most important public health problems.

Table 4. Epidemic dengue in Mexico, 1978 - 1987

00000000Puerto Rico represents another example of how the epidmiology of dengue has changed in recent years. Although earlier dengue epidemics must have occurred, the first one reported in the literature occurred in 1915(12). It was 30 years until the nest epidemic in 1945, and then a further 18 years until the next in 1963 (Table 5). The fourth major epidemic in Puerto Rico occurred six years later (1969) and, since then, endemic transmission has persisted on the island. Since 1977, Puerto Rico has experienced seven dengue epidemics caused by all four virus serotypes. Earlier epidemics were caused by a single virus serotype, but since late 1985, three virus serotypes (DEN-1, 2 and 4) have been transmitted simultaneously in Puerto Rico. Coincident with this hyperendemicity has been the emergence of DHF/DSS on the island.

Table 5. History of epidemic dengue in Puerto Rico

*Predominant dengue virus in years when multiple serotypes circulated.