Dengue is common throughout tropical and subtropical regions of the world. About half of the world’s population lives in areas suitable for DENV transmission and the main vector of dengue, the Aedes aegypti mosquito, is difficult to control and continues to expand its geographic range. Each year, up to 400 million people get infected with dengue viruses. Approximately 100 million people get sick from infection, and about 40,000 die from severe dengue.
Dengue is endemic in the United States territories and freely associated states of Puerto Rico, American Samoa, the U.S. Virgin Islands, the Federated States of Micronesia, the Republic of Marshall Islands, and the Republic of Palau. CDC classifies an area as endemic for dengue if the area has frequent or continuous dengue transmission, with evidence of more than 10 dengue cases in at least three of the previous 10 years. Dengue epidemics occur in a cyclical pattern every 3–7 years, with all four DENV serotypes reported in the Pacific Islands and the Caribbean. Limited surveillance data are available from the Federated States of Micronesia, the Republic of Marshall Islands, and the Republic of Palau.
Dengue can cause outbreaks with high numbers of cases in some years. In 2021, only 435 cases were reported in US territories, and 63 cases were reported in U.S. states. About 90% of the population at risk for dengue in US territories live in Puerto Rico. From 2010-20, approximately 95% of locally acquired dengue cases in the US occurred in Puerto Rico (29,779 cases), with the most cases and hospitalizations in Puerto Rico occurring among adolescents age 10 through 19 years (11,000 cases leading to 4,000 hospitalizations). Small convenience studies of children ages 9 through 16 conducted during vaccine trials estimated that 50% to 56% of children in this age group showed serologic evidence of past DENV infection. Dengue is not endemic in the continental United States or Hawaii; however, outbreaks and travel-associated cases have occurred in Texas, Florida, and Hawaii in recent years.