More than 1,000 blood donors have tested positive for West Nile virus in the United States, making the mosquito-borne disease one of the most common illnesses that can be acquired through transfusions, the Centers for Disease Control and Prevention said Monday.
“It is rather shocking,” Dr. Lyle Petersen, a West Nile virus expert with the CDC, said in a telephone interview on the opening day of the American Mosquito Control Association’s annual meeting in Savannah, Ga.
Petersen said the infected blood had been weeded out of the blood supply by new screening tests introduced in the United States last summer.
“The screening has substantially improved the safety of the blood supply, but the risk is not zero,” Petersen said.
Two people who received transfusions last summer are known to have contracted West Nile encephalitis, one of the more serious symptoms of the potentially fatal disease. Almost two dozen Americans caught the virus from transfusions in 2002.
Petersen said the manufacturers of the screening kits, U.S.-based Chiron Corp. and Roche Diagnostics, a unit of Swiss pharmaceutical giant Roche Holding AG, were working to improve the tests’ ability to detect the low levels of West Nile usually present in infected blood.
About 4.5 million Americans receive blood or blood products annually.
'This isn't going away'
Most people bitten by a mosquito carrying the virus suffer nothing more than headaches and flu-like symptoms, but the elderly, chronically ill and those with weak immune systems can develop fatal encephalitis and meningitis when infected.
A total of 230 people died and about 9,000 others contracted West Nile in 46 states and the District of Columbia last year. Only Alaska, Hawaii, Oregon and Washington State reported no human cases in 2003.
The 2002 outbreak infected 4,156 people, including 284 who subsequently died.
The CDC believes the increase in reported cases was due to heightened vigilance by the public and health-care community. The Atlanta-based agency, however, expects the virus, which first surfaced in the United States in 1999, to continue spreading this summer.
“This isn’t going away,” Petersen said.