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Woman Claims West Nile From Sex
CDC Provides West Nile Virus Update
CDC sees transfusion ties to West Nile
Bites from infected mosquitoes cause the majority of cases, but smaller numbers of people appear to have contracted the disease via transplanted organs and blood transfusions, said Dr. Jeffrey Goodman of the Food and Drug Administration's Center for Biologics Evaluation and Research.
The Centers for Disease Control and Prevention published the findings of seven investigations where such modes of transmission are suspected of causing the virus.
Results are not conclusive, but "it is most prudent to assume that blood-borne transmission likely has occurred," Goodman said.
Until the true risk is determined, the CDC is urging doctors of patients with the virus to report the cases to the disease agency so that all blood products from those patients can be withdrawn.
In addition, the FDA is working with blood banks to provide guidance, he said.
The virus has killed 84 of the 1,745 people infected this year, according to the CDC.
North Carolina has reported its first case, bringing the spread of West Nile to 36 states and the District of Columbia, said Dr. Lyle Petersen, a CDC epidemiologist.
The only test for West Nile virus available checks blood for the presence of antibodies, not the virus itself.
Researchers want to devise a test to find West Nile virus in the blood because it can be present without the presence of antibodies. In addition, infected donors might not have symptoms.
Tests carried out on people during the 1950s indicate that the virus remains in the blood for only a few days.
Antibody tests can indicate whether a person has ever been exposed to the virus, but presence of antibodies alone does not indicate blood is unsafe.
Researchers are exploring the possibility of treating blood products to kill the virus, called pathogen inactivation, Petersen said.
Still, he added, it is important to keep even poorly understood risks in perspective. Each year, about 4.5 million people in the United States receive blood products, many of them lifesaving.
West Nile virus was first detected in the United States in 1999 when it killed seven people in New York.
This year's outbreak has probably peaked in the South, Petersen said.
"However, a significant number of infections are still occurring, and people still have to be vigilant," he added.
Petersen said it is not clear whether the disease has peaked in the northern part of the country.