The Centers for Disease Control and Prevention (CDC) had reported that blood screening for West Nile Virus (WNV) has improved safety, but that a small risk of transfusion-associated transmission remains. In June 2003, blood collection agencies began using an investigational test to screen all blood donations for WNV and identify potentially infectious donations. About 6 million units of blood were tested from June to December 2003, and at least 818 donations were removed from the blood supply because they contained viruses. Six cases of transfusion-associated WNV transmission were reported, indicating low levels of the virus in blood components might escape detection.

CDC said the blood collection community and public health authorities will consider this data when developing screening strategies for 2004. The agency said the benefits of receiving needed blood transfusions outweigh the potential risk for WNV infection, although patients needing blood transfusions should be aware of the limited risk.

For more, see the Morbidity and Mortality Weekly Report at http://www.cdc.gov/mmwr.