Invisible threat. FDA wants to begin testing the nation's blood supply for West Nile virus.

Shielding Blood From West Nile

GAITHERSBURG, MARYLAND--With the 2003 West Nile virus season looming, the blood-transfusion community is racing to develop and deploy tests that will protect the nation's blood supply from the virus. At a Food and Drug Administration (FDA) meeting here yesterday, scientists and FDA officials expressed guarded optimism that tests will be ready on time. But committee members were confused about the threat the virus poses and how best to protect transfusion recipients from it.

The toll of last season's West Nile epidemic, which began in May, was by far the worst the United States has seen: more than 4000 infections and 267 deaths spread across 39 states. West Nile experts were shaken further when cases of transmission by blood transfusion emerged. Twenty-one such cases have since been confirmed by the Centers for Disease Control and Prevention, with another 21 possible cases. That was enough to prompt FDA in November to call for the rapid development of a West Nile blood test for the 2003 season.

So far, everything seems to be going according to schedule. Roche and a GenProbe-Chiron alliance are both racing to have tests ready for widespread use by 1 July. Both teams have been developing tests that represent a major shift in how blood is screened for pathogens because they directly measure levels of the virus. Today, blood banks rely heavily on antibody tests, which detect whether a person's immune system has mounted an attack on a specific invader. But CDC reported at the meeting that all of the known West Nile transfusion cases received blood from people who were antibody negative--presumably because the donors were recently infected and hadn't yet produced antibodies, a supposition that supports the idea that testing virus levels may be a better way to go.

Although FDA has proposed confining testing to certain seasons and geographic areas where West Nile risk is highest, its advisory committee had concerns about that approach. "We have long established in our country that blood is collected under a single standard," said council member James Allen, president and CEO of the American Social Health Association in Durham, North Carolina.

There was wide agreement that this rush to guard the blood supply is unprecedented. "Normally, you'd spend a couple years testing thousands and thousands of donors" before applying a new test to the entire blood supply, says Jeffrey McCullough, a transfusion medicine expert at the University of Minnesota, Twin Cities. But even though no one can predict the magnitude of this year's epidemic, the companies "just don't have time" to take the traditional route.

Related sites
FDA information on West Nile and blood
CDC information on West Nile