By Shaun Boyd
DENVER (KCNC/CNN) - The Centers for Disease Control says a blood screening missed trace amounts of West Nile virus. A transfusion of that blood led to the death of a cancer patient in Denver last year.
Bonfils Blood Center says the donor was a regular. He'd given platelets and plasma seven times in three months, showing no signs of West Nile.
"The majority of people who develop West Nile Virus don't become ill," said epidemiologist John Pape.
Pape says up to 80 percent of people who get West Nile show no symptoms, and because the virus is in the blood, blood banks are required to screen for it.
The first screening: a pool of six donors. If that's positive, the samples are tested individually with a more precise measure.
In this case, the pool sample tested positive, but the more sensitive test showed negative, so the blood was sent to area hospitals.
The CDC says it's never happened before.
"The virus was at such a small amount that the testing was not able to pick it up or pick it up and give discrepant or inconsistent results," said Dr. Tuan Le.
Le, the medical director at Bonfils, says it was only after the patient died that the plasma and platelets tested positive, and even then, he says the results were inconsistent.
Reporter: "At the time, is there anything they could have done, should have done to prevent this? Did Bonfils do everything?"
"They did everything strictly by the book," said Le.
It is a case, Le says, of a perfect storm.
"I think it's unfortunate, of course, because it involved a sick patient," said Le.
The blood center says from now on, when samples test positive, they will be discarded without the need for a second screening.