WASHINGTON (AP) – People with signs of West Nile infection, including headache and fever, should be barred from donating blood until nearly two months after the symptoms wane, federal health officials proposed Friday.

A Food and Drug Administration official briefed the agency’s Blood Products advisory committee about the recommendation. Depending on its effect on the blood supply, the guidance could be finished as early as this fall.

Already, West Nile is racing through this summer’s hot spots, sickening and killing people in Arizona, California and Colorado. Sensitive tests have tagged 61 potentially infected donors, whose blood donations were yanked from shelves, Hira Nakhasi, director of the FDA’s Division of Emerging and Transfusion Transmitted Diseases, told the advisory committee.

Typically, those donors could not make another blood donation until 28 days after their first symptoms of West Nile. That deferral period was based on 1950s research that indicated West Nile virus could remain in the body for 28 days.

The American Red Cross, testing samples from the 2003 West Nile epidemic, found the infectious virus could linger in blood for up to 49 days.

“This is all new territory,” Nakhasi told The Associated Press.

Within the FDA, researchers are mulling a change that would postpone potential donations until 56 days after West Nile diagnosis or symptoms consistent with the mosquito-borne ailment.

The FDA’s most worrisome concern with the proposed change: Reducing blood donations.

“That is the question we are discussing at the moment,” Nakhasi said.

The American Red Cross, which issued an urgent call for blood donations last week in its upstate region, said the recommendation would have “minimal” impact on blood supply.

“There are a small amount of people who are deferred,” said Stephanie Millian, a Red Cross spokeswoman in the agency’s national headquarters. “If they do make the recommendation, it would have a minimal impact.”

Whole blood donors already wait 56 days before rolling up a sleeve for the next donation. People who donate just platelets, the part of the blood that helps with clotting, however, would no longer be able to do so every two weeks.

America’s Blood Centers said it deferred 2,000 potential donors last summer. That shaved an estimated 3,200 units from the 7.5 million units of blood ABC collects annually in the United States and Canada. The new proposal would not have much of an effect nationally, despite summertime supply shortages, said spokeswoman Sharon Pavlovsky.

The sharper pinch would be felt regionally, especially in West Nile hot zones like Arizona. Nearly one-third of potential blood donations that initially tested positive for West Nile so far this summer were in Arizona, a state with 137 human infections as of July 22.

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