Aerial spraying of insecticides over Wynwood in August was so successful at interrupting the spread of Zika that federal health officials on Friday heralded the approach as “a new era” in the fight against mosquito-borne diseases — even as a local biologist who reviewed Miami-Dade surveillance data said that the air attack did not work as well as advertised.
As Zika continued to spread in a 4.5-square-mile area of Miami Beach, where the health department reported three more local infections on Friday, Centers for Disease Control and Prevention Director Tom Frieden delivered a cautiously enthusiastic endorsement of aerial spraying with two different pesticides — one that takes out adult mosquitoes, the other that kills eggs and larvae.
In a teleconference with State Surgeon General Celeste Philip, Frieden highlighted a new CDC report co-authored by Florida scientists showing that the combined aerial approach delivered results that on-the-ground efforts alone, such as truck spraying and backpack fogging, could not have accomplished in Wynwood.
“We cannot know with certainty that the control measures ended transmission, and of course the virus could come back tomorrow,” Frieden said, noting that the CDC report was not based on a controlled study but rather “a rigorous analysis” of mosquito surveillance data from Wynwood.
“But, having said that,” he said, “the findings are clear. Despite extensive ground-based efforts, there remained large numbers of mosquitoes, and Zika continued to spread among people in the area. As soon as aerial spraying was done, mosquito populations plummeted and monitoring found no more people infected in the weeks after the aerial application.”
On Sept. 19, the CDC lifted a travel advisory that warned pregnant women to avoid the area because the Florida Department of Health had not found any new mosquito-borne Zika infections in 45 days — meeting the federal agency’s standards for suggesting that mosquito-borne transmission of the disease is no longer occurring.
30 Number of people with mosquito-borne Zika infections linked to Wynwood
Though no new Zika infections have been reported in Wynwood since early August, Philip Stoddard, a Florida International University biology professor and the mayor of South Miami, said the evidence that aerial spraying significantly reduced mosquito counts in the area is not so clear cut.
Stoddard said he had not yet seen the CDC report on Friday. But he has reviewed Miami-Dade mosquito surveillance data for Wynwood gathered during roughly the same period — July 27 through Sept. 9 — examined in the CDC’s report.
He produced a study, which has yet to be published, and found that four rounds of aerial spraying of the pesticide naled over Wynwood did not have a lasting effect.
“If they can find something that works, God bless them,” he said. “But the naled started showing a lot of promise and then it stopped working. This is a problem.”
Stoddard said there was a decline in Wynwood’s mosquito counts associated with spraying of the larvacide BTI. But he added that other efforts, such as a door-to-door campaign to remove standing water and other mosquito breeding grounds, may have had a bigger impact.
“I’m encouraged by the BTI findings,” he said. “But you can’t be sure the BTI is what was doing it.”
As soon as aerial spraying was done, mosquito populations plummeted.
CDC Director Tom Frieden
For the uncertainty, Stoddard blamed federal and state health officials for not designing a more rigorous study of the ongoing public health crisis, which has led to more than 105 local mosquito-borne infections, most of those in Miami-Dade. An additional 773 travel-related Zika cases also have been reported in Florida, including 90 pregnant women.
“They dropped the ball,” he said. “They did not design a controlled test. These data are extremely important, and you would think they would have a statistician to help them design a study that would have given them the information they needed. But they did not do that.”
During the news conference, Frieden repeatedly stated that the CDC report produced by Florida officials was not a controlled study. He also emphasized that what worked in Wynwood may not work in other areas, including Miami Beach. Stoddard said his review found naled alone “never worked in Miami Beach.”
Still, Frieden said the data strongly suggested that the combination of naled and BTI had emerged as a new weapon in the fight against Zika and other mosquito-borne diseases.
“In the balance between protecting pregnant women and the next generation against devastating birth defects, we’re encouraged that there is now a new tool that appears to have had such dramatic results in Wynwood.”
Zika cases reported in Florida as of Sept. 23
Number of Cases
Total cases not involving pregnant women
. . .
. . .
Cases involving pregnant women regardless of symptoms*
* Counties of pregnant women are not disclosed.
** Does not include local cases
Source: Florida Department of Health