THURSDAY, Sept. 18, 2003 (HealthDayNews) -- The New England Journal of Medicine has made official what most of us already knew: West Nile virus can be transmitted through blood transfusions, and screening the blood supply is greatly reducing the risk of such transmissions.
The findings appear in the Sept. 25 issue of the journal. But they are being released Thursday to coincide with a meeting of the U.S. Food and Drug Administration's (FDA) Blood Products Advisory Committee, which is expected to discuss the safety of the nation's blood supply.
"Anybody who lives in the U.S. right now is concerned about the potential for transmission, and they should be, [but] the screening appears to be very effective," says Dawn Wesson, an associate professor of tropical medicine at Tulane University School of Public Health and Tropical Medicine in New Orleans.
"I don't think there's anything new in the report. It really does a nice job of summarizing the rapidity with which a number of different public and private agencies came together to get [blood] screening in place," Wesson adds.
West Nile virus, transmitted to humans via mosquitoes, can cause flu-like symptoms including fever and headache and, in a lesser number of people, encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).
The first case in the United States was reported in 1999 in New York City. Since then, the virus has spread steadily westward. So far this year, 4,137 human cases have been reported in 37 states. Those infection figures should easily surpass last year's, when 4,156 cases were reported. However, so far this year West Nile has been less deadly: 80 deaths to date, compared to 284 in 2002.
The first case of transmission of West Nile virus by blood transfusion was reported at the end of August 2002 in a woman who had received donated blood during an obstetrical procedure. Even before then, however, U.S. health officials were looking into ways to screen the blood supply.
The Sept. 18 issue of the CDC publication Morbidity and Mortality Weekly Report reports that, so far this year, two people have contracted West Nile virus, apparently from tainted blood samples that slipped past new testing procedures. One of the cases, however, may have been due to blood products that were donated before testing was in place. Both individuals, a 71-year-old Texas man and an 80-year-old Nebraska man, developed encephalitis but are recovering.
Federal officials are quick to point out that testing has been largely successful. "[The test] is a major step forward in protecting the blood supply but it's not perfect," said CDC director Dr. Julie Gerberding at a news conference Thursday. "It's a very low risk, but it's not a zero risk."
Dr. Jesse Goodman, director of the FDA's Center for Biologics Evaluation and Research, pointed out at the same news conference that each unit of donated blood goes to about two people. Since 600 units of blood have been pulled so far this year, "we can presume that we've prevented a very large number of infections and some significant amount of clinical disease," he says.
The authors of the new study confirmed that 23 patients had contracted West Nile through transfused blood or blood products in 2002. Ten of these people (43 percent) had suppressed immune systems due to an organ transplant or cancer, and eight (35 percent) were 70 years or older. The 23 cases were linked to 16 donors.
It's likely there were more than 23 cases of people who contracted West Nile through blood donations last year, say the study authors, who included federal and state health officials.
"The presumption is that there were some cases without symptoms and some with symptoms where the relationship wasn't recognized," says Dr. Louis Katz, president of America's Blood Centers, headquartered in Washington, D.C.
New tests to detect the virus in blood supplies became available early this summer under FDA Investigational New Drug (IND) protocols. Blood supply experts have hailed the rapid development of the tests as an extraordinary achievement.
According to the study authors, as of July 14, 2003, all civilian blood donations collected in the United States and Puerto Rico had been screened for West Nile virus with the use of these "investigational nucleic acidamplification" tests. A total of 163 donations out of some 1 million screened were found to have West Nile virus and were removed from circulation.
Epidemiologists at the U.S. Centers for Disease Control and Prevention (CDC) estimate that transmission of West Nile virus via transfusions peaked during the 1999 season and may have been as high as one in 5,000 donations.
Individual blood donations are being tested in Kansas, Nebraska, North Dakota, Oklahoma, and South Dakota. More routinely, however, blood donations are pooled in groups of six or 16 and then tested as one unit.
"Obviously there's a dilution factor that's involved. We know that by doing it the way we need to do it in order to get it done at all, we're probably missing some cases," Katz says.
"We're now trying to estimate how many we're missing," Katz says.
Nevertheless, the chances of contracting West Nile from a blood donation are "microscopic," he says. "If you need a transfusion, West Nile should not deter you."
More information
For more on West Nile virus, visit the U.S. Centers for Disease Control and Prevention. For more on the safety of the blood supply, try the American Association of Blood Banks.
