Persons were classified as negative for dengue infection if they had at least 1 specimen collected 6-60 days after illness onset that was IgM negative or a first specimen collected >60 days after illness onset that was IgG negative. Persons were classified as indeterminate for dengue infection if all specimens were collected <6 days after illness onset and were negative for virus isolation and for anti-dengue IgM. Imported dengue was defined as illness in a person with laboratory evidence of recent dengue infection and a history of international travel within 14 days of illness onset.