Florida health officials report on response to Zika in Wynwood; evidence shows aerial spraying likely helped interrupt local transmission

Florida health officials’ response this summer to the first identified cases of local transmission and the first identified outbreak of Zika virus infection in the continental United States, including aggressive mosquito control efforts, helped to interrupt local transmission and reduce the effect on the community, including pregnant women.

During late June through early August, 29 people were identified as having been infected with Zika virus through local mosquito-borne transmission, including 28 in Miami-Dade County and one in Broward County. Two cases were considered to be isolated with evidence of further transmission. However, the Florida Department  of Health (FL DOH) identified an area of the Wynwood neighborhood with a cluster of cases, indicating ongoing spread of Zika virus by mosquitoes.  Surveillance data showed intense transmission at a worksite and in the community. Although the outbreak was focalized, it continued to spread despite intense ground-based mosquito elimination efforts. Transmission rapidly ceased after Florida health officials implemented an aerial spraying plan that included use of the pesticides naled and bacillus Thuringensis to kill both adult mosquitoes and larva.

“After mosquitoes persisted and infections continued despite ground-based spraying, aerial spraying knocked down mosquitos rapidly and was associated with interrupting transmission of Zika in Wynwood,” said CDC Director Tom Frieden, M.D., M.P.H. “When faced with the potentially devastating outcomes of microcephaly or other serious brain defects that Zika can cause during pregnancy, we must use the best available tools to prevent infection. According to EPA assessments, when used properly, aerial spraying with naled for mosquito control doesn’t pose a risk to people or the environment.”

No new cases of locally transmitted Zika have been reported in the Wynwood-designated area since early August. As of September 19, the FL DOH has determined that active Zika virus transmission is no longer ongoing in the Wynwood area.

The FL DOH describes these investigations of mosquito-borne local transmission in this week’s MMWR (www.cdc.gov/mmwr).

CDC continues to work closely with Florida to identify and prevent ongoing Zika virus transmission in Miami Beach. Mosquito season in southern Florida continues through the fall, so additional cases could be identified. CDC recommends that people living in or traveling to Miami-Dade County strictly follow steps to prevent mosquito bites. Pregnant women should avoid travel to the identified 4.5-square-mile area of Miami Beach located in Miami-Dade County where active Zika virus transmission is ongoing. Pregnant women and their sexual partners who are concerned about potential Zika virus exposure may also consider postponing nonessential travel to all other parts of Miami-Dade County. CDC also advises state and local health departments to continue monitoring the area for any new evidence of active Zika virus transmission.

For more information about Zika: www.cdc.gov/zika/.

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U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES