Synopsis for April 9, 2004

The MMWR is embargoed until Thursday, 12 PM EST.

1. Update: West Nile Virus Screening of Blood Donations and Transfusion-Associated Transmission ― United States, 2003
2. Update: Influenza Activity ― United States, 2003-04 Season

Synopsis for April 9, 2004

Update: West Nile Virus Screening of Blood Donations and Transfusion-Associated Transmission ― United States, 2003

Although blood screening for WNV helped prevent many WNV infections, a small risk of WNV transfusion-associated transmission exists; however, to address this risk, changes to the blood screening strategies are planned for 2004.

Although mosquitoes are the most common route of infection with West Nile Virus (WNV), some WNV infections acquired through blood transfusions were documented in 2002. In 2003, FDA, CDC and the blood collection community responded quickly by implementing experimental WNV blood screening. This screening successfully identified more than 800 blood donations containing virus, possibly preventing more than 1,000 infectious transfusions derived from those donations. Despite this success, CDC confirmed that six people were infected with WNV by blood transfusion during 2003. The blood these patients received had been screened for WNV, but the virus concentrations in that blood were not detected by the screening tests. Changes in WNV blood screening strategies will be implemented in 2004. For people who need blood transfusions, the chance of getting a transfusion containing infectious WNV is small.

Update: Influenza Activity ― United States, 2003-04 Season

While the U.S. influenza season was earlier and more severe than the previous three seasons, it was comparable to several seasons in the 1990's in which similar influenza virus strains circulated.

The 2003-04 influenza season in the United States began, peaked and ended earlier than usual. The predominant influenza virus strain belonged to a subtype called influenza A (H3N2). While the season was more severe than the previous three seasons, it was within the expected range for typical A (H3N2) seasons, which were common in the late 1990's. CDC received reports from state health departments on 142 influenza-associated deaths in children this season. Almost all occurred before the end of January. Whether this is more or less than usual cannot be known, as national data on this condition have never been collected before. CDC is now working with state epidemiologists to track this information annually. This year’s avian influenza outbreaks in poultry in North America have not caused any human infections and none of the outbreaks are related to the avian influenza outbreaks in Asia.

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