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THURSDAY, Aug. 14, 2003 (HealthDayNews) -- The number of reported cases of West Nile virus continues to multiply, but U.S. health officials said Thursday that a new test to screen donated blood has probably prevented even more infections.
The number of human cases shot up nationwide from 153 a week ago to 393 as of late Wednesday, including nine deaths, the Centers for Disease Control and Prevention reports. Only last week, officials had announced a tripling in the number of infections as the mosquito-borne disease entered its high season.
But the development of a test that finds West Nile's genetic material in donated blood appears to be stemming the tide somewhat. Since mid-July, 1.1 million units of blood have been donated, and the test found that 163 of those units repeatedly tested positive for those genes, said Dr. Anthony Marfin, acting deputy director of the CDC's Division of Vector-Borne Infectious Diseases.
Last year, 23 people were infected with the virus after having received transfusions of donated blood. Since then, the government and blood collection agencies have developed the test. They have also asked donors whether they have suffered recently from fever or a flu-like illness -- which could indicate a West Nile infection -- and delay collecting their blood if they answer yes.
Most of those donors have shown no symptoms of disease yet, but follow-up tests are being done.
"Some have developed West Nile fever," Marfin said. "We know that at least one has developed West Nile encephalitis."
The blood was taken out of the donor pool once the virus was detected, Marfin added.
Also last year, health officials found for the first time that the virus can also be transmitted through donor organs. No quick test is available to screen the organs yet, they said.
Meanwhile, the disease has infected people in 23 states so far, according to Dr. Stephen Ostroff, deputy director of the CDC's National Center for Infectious Diseases. "Based on what we see at this point, it looks like we're progressing pretty much apace" as last year, he said, which had a rate he called "unprecedented."
However, the virus is taking a different route. Last year the outbreaks were worst around the Mississippi Delta. So far this year states in the Rocky Mountains and the plains are taking a hit. Colorado alone has almost half the cases and five deaths, followed by South Dakota and Texas, according to the CDC. Ostroff added that the virus was making its way coast to coast, with Arizona reporting its first animal case.
Ostroff said he expected the numbers to climb through September because the virus is "just now getting into the peak period."
"West Nile is really picking up momentum in the United States," he said.
Officials stress that the best way to avoid West Nile is to avoid mosquitoes. Stay indoors at dawn and dusk, when the pests are most active. If you can bear to not bare your arms and legs in the summer, wear long-sleeved shirts and long pants. Use repellants with DEET. Dump any standing water around your home, even from a soda can.
More information
Get the lowdown on West Nile virus from the Centers for Disease Control and Prevention. For more on the safety of the blood supply, try the American Association of Blood Banks.
