KEY WEST, Fla. (AP) -- Key West's health officials were urging people on Friday to take precautions against dengue (DEHN'-gay) fever after survey results showed that 41 percent of 240 local residents tested positive for antibodies associated with the disease.

Dengue fever is a flulike illness spread by the bite of an infected Aedes aegypti mosquito, a common urban mosquito in the United States and the Caribbean. It is also known as breakbone fever because of the intense joint pain suffered in extreme cases.

Results show that 99 of 240 residents who donated blood for the survey by the Centers for Disease Control and Prevention and the Florida Department of Health tested positive for Flavivirus antibodies, which can include dengue antibodies.

The survey was launched after three confirmed cases of dengue surfaced in Old Town Key West in August, the first locally acquired cases of the mosquito-borne illness reported in the state in more than 40 years.

Eight of the people who tested positive for the antibody are thought to have contracted the virus locally in Key West within the last three months. All have fully recovered, health officials said Friday during a conference call. No more cases have been reported, and the virus was confined to the Key West area.

"The results are significant in that they indicate the virus is present in Key West," said Monroe County Health Department Administrator Bob Eadie. He urged residents to protect themselves and their families, but without rearranging their daily routine.

"Many cities in the world suffer from a great deal more exposure to the disease than Key West and yet continue to function normally," he said.

Residents should take precautions by avoiding being bitten by mosquitoes and, most importantly, to drain all standing water near houses, health officials said.

Researchers from the Centers for Disease Control and Prevention and the Florida Department of Health conducted the survey with help from the Monroe County Health Department and the Florida Keys Mosquito Control District from September 23 to 27.

The process of notifying survey participants was under way.

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