On Friday, Florida Governor Rick Scott announced that the Department of Health (DOH) has concluded that four cases of the Zika virus are likely mosquito-borne.  One of these cases involves a woman and the other three cases involve men.

Thomas Frieden/CDC
Thomas Frieden/CDC

At this time, DOH believes that active transmissions of the Zika virus are occurring in one small area in Miami-Dade County, just north of downtown.

The announcement prompted a news conference by the Centers for Disease Control and Prevention (CDC) yesterday, in which Director Dr Tom Frieden said, “These cases are not unexpected.  At CDC, we’ve been saying for months based on experience with Chikungunya and Dengue which are viruses spread by the same mosquito that spreads Zika, that individual cases and potentially small clusters of Zika are possible in the U.S. As we have anticipated, Zika is now here.

As a reminder, after local transmission of chikungunya was detected in Dec. 2013 and spread wildly through Latin America and the Caribbean and more than 1.1 million suspected and confirmed cases were reported through 2014, Florida was the only US state to report local transmission, 12 cases total.

“We are proceeding as though the cases are confirmed local Mosquito-borne transmission.  To be clear about this because it can be confusing, confirming mosquito-borne transmission is not as easy as confirming infection in a person.

“Our best evidence would be if we found Zika in one of the Aedes aegypti mosquitoes in the area where there are cases reported. But that is very difficult to do, it is like finding a needle in a hay stack.  Whether — if infected mosquitoes are not found, that doesn’t imply that it’s not spreading by mosquitoes. If they are found that’s highly suggestive. But it’s not expected that we would find infected mosquitoes even if there is spread by mosquitoes in that area.”

Dr Frieden gave props to Florida health officials saying, “We’re working closely with Florida and we’ve been impressed by the comprehensiveness of their investigation.”

Gov Scott talked of the state’s efforts saying, “Since our first travel-related case in February, Florida has taken an aggressive approach and committed state and local resources to combat this virus. Just like with a hurricane, we have worked hard to stay ahead of the spread of Zika and prepare for the worst, even as we hope for the best.  Now that Florida has become the first state to have a local transmission, likely through a mosquito, we will continue to put every resource available to fighting the spread of Zika in our state.”

As of July 27, 2016, 1,658 cases of Zika have been reported to CDC in the continental United States and Hawaii; none of these were the result of local spread by mosquitoes. These cases include 15 believed to be the result of sexual transmission and one that was the result of a laboratory exposure.  This number does not include the four Florida cases likely caused by local transmission.