Dengue outbreaks in Guánica-Ensenada and Villalba, Puerto Rico, 1972-1973.

Epidemics of dengue fever occurring in Puerto Rico in 1963 to 1964 and 1969 were caused by dengue-3 and dengue-2 (DN-2) viruses, respectively, but endemic dengue transmission has never been documented on the Island. Since the 1969 epidemic, a surveillance system has detected DN-2 activity on the Island during each of the years 1970 through 1973, which suggests endemic persistence of the virus. This report describes the investigation of localized outbreaks of DN-2 in Guanica-Ensenada (1972) and Villalba (1973), and presents epidemiological, serological, and virological data from the outbreaks. Analysis of geographic distribution of dengue activity in Puerto Rico in recent years indicates that the DN-2 transmission in 1970 to 1973 may represent a long tail-off of the 1969 epidemic rather than the emergence of a truly endemic situation.