Chikungunya: 11 Locally Spread Cases Confirmed‏ in Florida

Troy Brown, RN

December 05, 2014

Chikungunya virus infection has now spread to the continental United States, according to a recent report from the Centers for Disease Control and Prevention. In addition, the agency reports that Chikungunya infection and transmission is widespread in Puerto Rico.

Katherine Kendrick, MPH, from the Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, and colleagues present their findings on transmission in Florida in an article published in the December 5 issue of the Morbidity and Mortality Weekly Report.

On June 27, 2014, the Florida Poison Information Center Network notified the Florida Department of Health in Miami-Dade County of a patient who was suspected of being infected with chikungunya virus. Further investigation and testing showed that the patient was the first case of locally acquired chikungunya in the continental United States.

Chikungunya virus and the four dengue viruses are spread by Aedes aegypti and Aedes albopictus mosquitoes, which are found in Puerto Rico and the tropics. Dengue virus infection does not provide long-term cross-protective immunity, and its victims are subject to severe infection if they are reinfected with another dengue virus. Chikungunya virus, in contrast, does provide long-term immunity.

The first locally acquired case of chikungunya virus infection in the Americas occurred on the Caribbean island of St. Martin in December 2013. Since then, the number of chikungunya cases among travelers returning from areas in which the virus is endemic has increased, especially in the Caribbean and South America. This number has been particularly large in Florida, which has seen a total of 272 imported cases from January 1 to October 14, 2014, compared with 1110 total cases reported in the other 47 contiguous states.

Since the June 27 report, 11 autochthonous chikungunya cases have occurred in four counties in South Florida, including two cases in Miami-Dade County, four in Palm Beach, four in St. Lucie, and one in Broward.

Of the 272 imported cases, 131 (48%) have been reported in Miami-Dade, Palm Beach, and Broward counties. All 11 locally acquired cases were confirmed by laboratory testing.

The source is unknown for two of the patients in St. Lucie Country, but they live within 1500 feet of each other, and proximity in space and time appears to be a factor.

Among cases believed to be imported, Haiti (38%) was the most common country of exposure, followed by the Dominican Republic (30%).

Surveillance related to local transmission of the virus has been conducted in 50- to 100-m clusters around a patient's residence and has included enhanced syndromic surveillance and medical record review.

Media coverage, reverse 911 dialing, and targeted mailings have been used to increase public awareness. Mosquito control workers have been sent to patients' residences before or on the same day counties became aware of positive laboratory test results.

Chikungunya virus shares the same vectors as dengue virus, so the surveillance activities and control efforts used in Florida can also benefit efforts throughout the United States, the authors write.

There is no vaccine to prevent chikungunya fever, so prevention efforts largely focus on avoiding mosquito bites, primarily during daylight hours. The Florida Department of Health and Centers for Disease Control and Prevention also suggest using air conditioning and window screens to prevent mosquitos from coming inside, keeping water containers empty, wearing long-sleeved shirts and long pants, and applying insect repellents.

In a separate report in the same issue of the Morbidity and Mortality Weekly Report, researchers describe the expanding disease activity in Puerto Rico. In January 2014, the Puerto Rico Department of Health and the Centers for Disease Control and Prevention included chikungunya virus in its existing Passive Dengue Surveillance System. Chikungunya virus was first identified in Puerto Rico in May 2014, and between then and mid-August, more than 10,000 cases were reported in 57 of Puerto Rico's 78 municipalities. Because there is no preexisting immunity against chikungunya virus, individuals who travel to that part of the Americas should use reasonable methods to avoid mosquito bites. The virus is expected to continue its spread throughout areas of the Americas where the mosquitoes that spread it reside.

Morb Mortal Wkly Rep. 2014;63:1121-1128. Full text

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