A woman planning a Florida vacation in Key West called the health department there last week to ask if it were true that the city was being evacuated because of an epidemic of dengue fever.

"No!" Chris Tittel, a spokesman for the Monroe County Health Department, says he told her. "No, no, no, no, no."

Dengue (pronounced DENG-gay) is a viral illness, spread by mosquitoes, that can cause fever, headaches, body aches and a rash. Symptoms range from mild to severe, although some people have no symptoms.

Without a doubt, there is dengue in Key West, although at 27 known cases last year and 18 so far this year, it is hardly what most people would call an epidemic. Those cases are the first outbreak in Florida since 1934, and some medical experts fear that the disease, once rampant on the Eastern Seaboard, could take hold again.

Parts of the Caribbean and Central America are having epidemics now, but none of those infected in Key West had traveled outside the country. That means they caught the virus locally.

News of the disease has apparently unsettled a few potential visitors. Tourism officials and business owners in Key West are even more unsettled, by the way the federal Centers for Disease Control and Prevention has publicized the cases.

On July 13, the centers issued a news release stating that an estimated 5 percent of Key West’s population showed evidence of recent exposure to the dengue virus. The estimate was based on tests of 240 residents, of whom 13 were positive. The 5 percent figure was reported by many outlets.

That news was the last thing the city needed, with the economy already making the usual summer slump in tourism even worse. The oil spill in the Gulf of Mexico has also scared some visitors away, even though the oil has been nowhere near Key West.

"I don’t know if the CDC understands what it potentially has done here," said Andy Newman, the director of media relations for the Florida Keys and the Key West tourism council. He said he knew of a "smattering" of canceled trips but suspected more.

Robert Eadie, administrator of the health department, called the disease centers’ report "very alarmist."

Local officials were irked that the centers had used just 240 people to estimate an exposure rate for the entire city, which has a population of about 25,000.

Scientists involved in the research are sticking to their story. Dr. Harold Margolis, chief of the disease centers’ dengue branch in Puerto Rico, said it was statistically valid to extrapolate from the 240 people tested.

"Somehow the virus is getting there," Margolis said.

An infected visitor may have passed the virus to local mosquitoes, or a mosquito carrying dengue may have arrived on an airplane or cruise ship. Key West has plenty of Aedes aegypti, a type of mosquito that can carry dengue. People are worried about being stigmatized, especially those with businesses. A restaurant owner who was infected a year ago agreed to be interviewed only if his name was not published, because he thought fear of the disease might keep customers away, even though the virus is not spread by food or personal contact. He said he had had a mild flulike illness for about five days. He had no idea it was dengue until health workers asked him to be tested. Then they urged him to avoid being exposed again, because there are four strains, and people who have had one strain and later contract another can develop a dangerous form of the disease that can cause hemorrhaging and even death.

Dr. Peter J. Hotez, a tropical medicine expert at George Washington University, said he thought the potential was "pretty high" for dengue to spread up the Gulf Coast, where another species of Aedes mosquito that can carry the virus is common. If the disease does get there, it will strike poor people hardest, he predicted, because many of them lack screens and air-conditioning. There is no vaccine.

"I believe the threat is very real," he said. "And we understand that the CDC is about to close its dengue branch. Can you imagine anything so stupid? This is the worst time possible."

The disease centers confirmed that the 2011 budget does eliminate financing for the "vector-borne" disease branch, which tracks dengue, West Nile virus, plague, encephalitis and other illnesses carried by insects.

Dr. Ali S. Khan, deputy director of the National Center for Emerging and Zoonotic Infectious Diseases, said that the disease centers had to make budget cuts, and that the vector-borne disease branch was one. But he said other money could be used to pay for some of the work it used to do.

More than a dozen medical organizations have signed a letter to Congress, asking that the money be reinstated.

Meanwhile, as they are trying to ease public fears, officials in Key West are scrambling to stop the outbreak. The best way to fight the disease is to fight the mosquitoes, by wearing bug repellent, spraying pesticides and dumping anything that holds water. The amount it takes to fill a bottle cap is enough for Aedes aegypti to breed.

Mosquito control inspectors have been dispatched to neighborhoods with suspected cases. Sometimes they have to deal with vacant houses because Key West, like many cities, is dotted with foreclosures. The inspectors have also told landscapers to stock ponds with minnows, which feed on mosquito larvae. The city even launched Mosquito TV, a weekly show, to mobilize residents against the pest.

At the Key West Cemetery, where the gravestone of B.P. Roberts (who died in 1979) reads, "I told you I was sick," dozens of "ovitraps" — black plastic cups laced with poison to kill female mosquitoes and their eggs — mingled among concrete urns and vases of water rife with squiggling larvae. Plans for next year include providing sterile male mosquitoes to prevent their mates from reproducing.

Key West residents have been taking it all in stride. At a parade in October, a group calling itself Dengue Night Fever included a John Travolta look-alike and followers sporting giant mosquito wings.

Tourists interviewed this week at the nightly sunset celebration on Mallory Square seemed oblivious. Linwood Dean, 31, and his family had been visiting from Pennsylvania for three days. Linwood had a fresh mosquito bite on his forearm.

"We haven’t heard anything about it," he said. "We are having a wonderful time."

© 2010 The New York Times Company