Aerial spraying likely was key to eliminating the Zika outbreak in the Miami neighborhood of Wynwood, officials said as they defended the method amid skepticism from the public.
Wynwood was the first area in the U.S. to experience Zika transmission from mosquitoes, the primary mode of transmission, in July. About 30 people got the virus that can cause the birth defect microcephaly, but local officials say Zika is no longer spreading there after no new cases after 45 days.
The Centers for Disease Control and Prevention released a report on Friday detailing the agency’s response to the Wynwood outbreak.
CDC Director Tom Frieden said on a call with reporters that initial efforts, including truck spraying, to attack the mosquito population weren’t working.
“Despite extensive ground-based efforts, there remained large number of mosquitoes and Zika continue to spread,” he said.
But the CDC found success after using aerial spraying of an insecticide called Naled and the use of a larvacide called BTI that killed mosquito larvae.
“Mosquito populations plummeted, and monitoring found less people infected after aerial application,” Frieden said.
He added that it appears “very highly suggested that when the [spraying] was done by air there was a rapid knockdown.”
The CDC found that there were no increases in emergency room visits due to the aerial spraying. Those would include visits for wheezing, shortness of breath, nausea or vomiting.
The agency noted that only a small amount of the insecticide Naled was sprayed, about less than one ounce per acre of spraying.
However, some experts and people are skeptical about aerial spraying. Puerto Rico, which has more than 2,000 cases of local transmission, declined to pursue aerial spraying.
A recent op-ed in the Miami Herald pointed out that the European Union banned the use of Naled in 2012.
“The fact that these Naled exposures are so-called ‘low level’ and the pesticide is rapidly degraded outdoors is misleading because even low levels of [organophosphate] rapidly enter the brain and central nervous system via inhalation, ingestion and/or skin contact,” wrote Claudia Miller, professor at the University of Texas Health Science Center.
Frieden said that when aerial spraying is used per Environmental Protection Agency labeling, it is safe.
“We look at the use [of the insecticide] as it is used, not necessarily the chemical itself,” he said. “When used according to label instructions per EPA instructions it can be used safely.”
The product is not banned in Europe, just not registered with the European Union. The reason is a different infrastructure for mosquito control, and the company that makes Naled decided not to pursue registration, according to the EPA.
Zika is still spreading in the Miami area, as officials turn their attention to an outbreak in Miami Beach. Overall, Florida has found more than 80 non-travel-related cases in Miami-Dade County and other parts of the state.
Frieden conceded there are environmental conditions that make it more challenging to do aerial spraying in Miami Beach. However, the CDC has done some spraying and initial data “shows a similar rapid knockdown in mosquito populations.”
