Dengue occurs frequently or continuously in the U.S. territories of American Samoa, Puerto Rico, and the U.S. Virgin Islands, and in the freely associated states of the Federated States of Micronesia, the Republic of the Marshall Islands, and the Republic of Palau. Dengue is rare in the continental United States. Most dengue cases in the continental United States are imported cases. Imported cases happen when travelers become infected overseas, and then return to the United States.