Dengue virus reappears in Key West

ATLANTA — CDC officials are urging people in the South Florida area to protect themselves against mosquito bites, as they estimate that about 5% of the people there have shown evidence of dengue infection.

These most recent estimates, announced here at the 2010 International Conference on Emerging Infectious Diseases, are significantly higher than an earlier CDC report of more than two dozen cases of locally acquired dengue in Florida in the preceding 9 months. The cases are the first such cases reported in Key West, Fla., since 1934.

In September, three cases of confirmed dengue fever alerted researchers from the CDC and the Florida Department of Health to a possible outbreak. One case occurred in a New York state resident whose only recent travel had been to Key West, and the other two were noted in Key West residents.

“These cases represent the re-emergence of dengue fever in Florida and elsewhere in the United States after 75 years,” said Harold Margolis, MD, chief of the CDC’s dengue branch. “These people had not traveled outside of Florida, so we needed to determine if these cases are an isolated occurrence or if dengue has once again become endemic in the continental United States.”

To investigate, the researchers are conducting seroprevalence studies by administering a questionnaire designed to evaluate study participants’ previous exposure to dengue. Two hundred forty blood samples were also collected and tested for the virus or signs of previous infection.

Immunoglobulin G enzyme-linked immunosorbent assay results revealed that 41% of participants had evidence of previous infection, and 13 participants had evidence of either an acute, recent or presumptive recent dengue infection. A weighted estimate of acute and recent infection indicated that 4.9% (95% CI, 1.8-7.9) of Key West’s population was affected by the disease.

Reverse transcription polymerase chain reaction data also showed that dengue virus serotype 1 was responsible for one case of acute infection, and results from a plaque reduction neutralization test indicated that seven recent infections were also attributable to dengue virus serotype 1. Further analysis genetically linked this strain to a similar one that caused previous outbreaks in Mexico, the researchers noted.

“We’re concerned that if dengue gains a foothold in Key West, it will travel to other southern cities where the mosquito that transmits dengue is present, like Miami,” Margolis said, adding that monitoring in Florida is ongoing. “The mosquito that transmits dengue likes to bite in and around houses, during the day and at night when the lights are on. To protect you and your family, CDC recommends using repellent on your skin while indoors or out. And when possible, wear long sleeves and pants for additional protection.” – by Melissa Foster

For more information:

Gallagher GR. #247. Presented at: 2010 International Conference on Emerging Infectious Diseases; July 11-14, 2010; Atlanta.