Every year, nearly 14 million units of blood are collected from donors across the U.S., says the American Red Cross. It's a literal lifeline that accident victims, cancer patients and those heading into the operating room depend on daily. Every two seconds or so, in fact.
Which is why nobody wants the Zika virus swimming around in the blood supply.
Last week, the U.S. Food and Drug Administration took the extraordinary step of recommending that all blood donations be tested for the rapidly spreading and potentially deadly virus. The FDA outlined a program that will implement testing in all states and territories within the next 12 weeks.
But what about the blood already on hand? With hundreds of thousands of bags sitting around in coolers, is it possible that the Zika virus already has entered the U.S. blood supply?
Does that need to be tested, too?
"There is no recommendation to go back and test the supply on hand, because the actual recommendation is extremely precautionary," says Dr. Steven Kleinman, the senior medical adviser to the AABB (formerly the American Association of Blood Banks), the group that provides standards for transfusion medicine and cellular therapies and works closely with organizations like the Red Cross. "Right now we think the risk of contracting Zika virus from a blood transfusion in the U.S., under the current FDA guidance, is thought to be very, very low."
"No. 1, we have procedures in place to ask donors to defer themselves [not give blood] if they meet certain criteria," Kleinman says. "In addition, a number of states, such as Florida, are already doing the testing that is being recommended by FDA going forward. In the highest-risk areas, testing has already been implemented. Those two things together say that blood on the shelf is really quite safe."
The Zika virus, primarily spread by mosquitoes, is passed on through sexual contact of infected individuals and from mother to unborn child. It's been linked to severe brain damage in children in Brazil and, recently, to some neurological conditions in adults. Many people, however, have mild symptoms and don't even know they have it.
Zika probably can be spread through blood transfusions, too, according to the Centers for Disease Control and Prevention. Though the CDC says the virus currently poses a "low risk" of getting into the blood supply, the FDA clearly is taking no chances.
The FDA first issued guidance in February to protect the blood supply, calling for prescreening of potential donors. Those who wish to donate are asked about their travel to areas with Zika outbreaks and about contact with those who have been infected with the disease. Those deemed to be risks are turned away and asked not to donate for at least four weeks.
Then, in March, the first blood screen for Zika became available. Another was made available in June.
Last week's recommendations — that all donated whole blood and blood components undergo universal testing for Zika — was the latest step. It's necessary "in order to help maintain the safety of the U.S. blood supply," Luciana Borio, the FDA's acting chief scientist, said in a statement.
If the ambitious plan outlined by the FDA holds up, in 12 weeks every unit of blood donated in the U.S. will undergo testing for Zika virus. But that brings up another question or two: What about between now and then? Could the Zika virus still slip in?
It's extremely unlikely, Kleinman says. The prescreening and the actual blood testing for Zika that already is happening in places like Florida are effective. Rollouts for tests in other states where Zika could pop up — warmer, mosquito-friendly places — are scheduled soon, in the next four weeks. In 12 weeks, much of the U.S. will be in winter and out of mosquito season, when Zika is most likely to spread and, potentially, be spread to the blood supply.
All the concern over Zika isn't unprecedented. Several tests already are done on donated blood for infectious diseases including hepatitis B, hepatitis C, HIV, West Nile virus and syphilis. Those tests have proven extremely effective in keeping the blood supply clean and stopping the possible spread of those diseases via blood transfusions.
"To put it in perspective, based on what we currently know about the amount of Zika virus transmission in the U.S, as well as from returning travelers [from Zika-infected areas], I would say contracting Zika virus from a blood transfusion is less likely than contracting some of the other agents that we have been concerned about over the last 10-15 years, 20 years, and have also put in interventions for," Kleinman says. "I think West Nile virus was more of a risk. Certainly, if we go back years and years, hepatitis C and HIV were more of a risk."
So Zika might be scary, sure. But if you must worry, worry less about that blood transfusion you may need and more about finding some good mosquito repellent.