Key West physicians were also contacted to provide serum specimens from recent patients with symptoms consistent with dengue. Nine of 21 samples sent for testing came back positive for dengue.
The tally of confirmed dengue infections in Key West eventually grew to 28, with the most recent case diagnosed in mid-April.
Dengue is much more of a problem elsewhere in the hemisphere, with an estimated 4.6 million cases from 2000 to 2007 in Mexico, the Caribbean, and Central and South America, according to MMWR's editors.
But the Key West outbreak demonstrates the potential for significant penetration into the continental U.S., they suggested.
They noted that international travelers can pick up the virus in endemic areas, and are often still viremic when they return. In areas with mosquito species capable of transmitting the virus -- such as Aedes aegypti and Aedes albopictus, both present in the southern and southeastern U.S. -- dengue can then spread locally.
The editors also recommended that physicians consider dengue when evaluating any patient with a febrile illness who has recently been in subtropical areas of the U.S., as well as in countries to the south.
"This is particularly important when signs and symptoms such as thrombocytopenia, leukopenia, hemoconcentration, rash, or eye pain are present," they wrote.
Suspected cases should also be reported promptly to public health authorities, they indicated.
No external funding for the work was reported.
No potential conflicts of interest were reported.