Centers for Disease Control and Prevention (CDC) Director, Dr Thomas Frieden today gave a press conference concerning Zika virus infection in Puerto Rico and blood safety after returning from the island.


Frieden started the briefing with the following statement: “Based on the best information available, Zika infections appear to be increasing rapidly in Puerto Rico.  The implication of this and the real importance of this information is that in the coming months it’s possible that thousands of pregnant women in Puerto Rico could become infected with Zika.

“This could lead to dozens or hundreds of infants being born with microcephaly in the coming year and for the thousands of other infants born to women infected with Zika who don’t have microcephaly, we simply don’t know and may not know for years if there will be long-term consequences on brain development.”

He then shifted into the topic of Zika in the blood supply noting, “Since April 3, blood centers in Puerto Rico have screened locally collected blood for Zika, using a highly accurate nucleic acid amplification test, this is a test that measures for the actual virus in the blood.  It’s highly sensitive and highly specific.  Screening blood that’s donated for Zika protects the safety of patients and keeps the blood supply safe.  At the same time, it gives us a window to see what’s happening in infection rates generally, even though it’s not a random sample of society.

“A total of 68 out 12,777 blood donations in Puerto Rico have tested positive for Zika.” However, that number has increased steadily with 1.1 percent of blood donations testing positive for Zika just last week, the week ending June 11th.

To date no confirmed cases of Zika spread through a blood transfusion anywhere in the United States or Puerto Rico and the other territories.

Then Frieden went to where the blood testing and the pregnancy issue overlap: ”  The result of that is that a 1 percent positivity rate at any given time translates into a more than 1 percent, perhaps 2 percent, we don’t know exactly, rate of infection each month.  This means that over the course of many months, for example, a nine-month pregnancy, there would be a substantial chance that a woman would become infected.  I would reiterate that all donations that test positive are removed from the blood supply and donors who test positive get information about how to avoid spreading Zika to others.  The increase in blood donations testing positive in Puerto Rico is concerning.

“It likely reflects an increase in the general population, but our concern here is about protecting pregnant women.  With this rate of infection, the possibility that there could be thousands of pregnant women infected leading to dozens to hundreds of affected babies is what’s of most concern.”