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MIAMI (CBSMiami) — The FDA has confirmed to CBS4 News that donated units of blood in Florida have tested positive for the Zika virus.

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The FDA will not say where or when the tainted blood was discovered, but it is the first since one unit of Zika-infected blood was discovered at an undisclosed donation center in August.

Dr. Aileen Marty, a world renowned researcher at Florida International University, says there is good news and bad news in the FDA’s revelations.

“Finding it before it is used is very good, because that means we’re doing the right thing, we’re trying to verify whether there are any contaminated bloods before they are given,” she said.

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But Marty, who is working with a variety of health care agencies on the Zika crisis, worries about the accuracy of the experimental tests being used to detect Zika. She’s concerned about their reliability and the possibility of infected blood getting through.

“Just because the test is negative doesn’t necessarily mean that the blood is pure until you have double tested it with a different testing method to be sure that it is, in fact, free of Zika,” Marty said.

The three tests being used to screen for Zika in donated blood are not licensed by the FDA, but have been allowed into service on an emergency basis.

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An FDA spokesperson declined to discuss the screening protocols being used by testing labs, and how many are or are not using the double testing procedure, that Dr. Marty says has been recommended by the Centers For Disease Control.