Low Risk of West Nile Seen with Blood Transfusion

NEW YORK (Reuters Health) - With the introduction of a new test for West Nile virus (WNV) this season, the risk of infection from blood transfusions is "very low but not zero," the Centers for Disease Control and Prevention said during a press briefing on Thursday.

The CDC has learned of two cases of transfusion-related WNV infection. "These two individuals have all of the clinical criteria of transfusion-associated WNV infection...Thankfully, both have recovered," CDC director Dr. Julie Gerberding said.

In late June, blood-banking officials began screening blood for WNV. It's an effort that is paying off, Gerberding said. "Overall the test has identified more than 600 infected units of blood, which were pulled from the blood supply."

Currently, blood-banking agencies are testing pooled blood samples taken from 6 to 16 donors. "The blood is mixed together and then tested and if the pool is found to be positive, than the individual donors are evaluated," Gerberding said.

"This is a major step forward in protecting the blood supply but it is not perfect," she said. "Clinicians and public health officials need to be on the look out for cases of fever, headache, and (brain inflammation) in blood transfusion recipients so we can look back and make sure an infected unit didn't slip through the cracks."

The CDC is recommending, when feasible, the screening of individual units of donated blood. "In high-risk areas, this is being done," Gerberding noted. "This is not yet possible at every donation center. The test kits are not available and the testing takes time. We will get there, but we are not there yet."

During Thursday's briefing, Gerberding also updated reporters on what she called a "very important" outbreak of measles in the Marshall Islands in the Pacific Rim area.

As of September 13, a total of 647 cases have been diagnosed among area residents, 58 required hospitalization and 3 individuals have died from measles.

"Sadly," Gerberding said, "in this particular area the vaccine coverage was not adequate...so when measles was introduced from parts of Asia that continuously have outbreaks of measles, it very quickly spread through the population."

Before the outbreak, an estimated 75 percent of children had received the measles vaccine. "This is quite low," Gerberding said. With the CDC's help, coverage levels now stand at roughly 98 percent "so we expect to see cases of measles decline," she said.

This outbreak serves as a reminder that "we have to continue to be vigilant about making sure people everywhere understand the importance of measles vaccination," Gerberding said.

SOURCE: Morbidity and Mortality Weekly Report, September 19, 2003.