Information about West Nile Virus and Blood Safety
Background
The ongoing outbreak of West Nile virus (WNV) infections in the United States has raised concern that WNV could be transmitted through blood transfusion. In one recent cluster, 4 organ recipients from a single donor all developed clinical WNV infection and the donor's pre-donation blood contained WNV. The source of that donor's infection continues under investigation but may have been either natural or related to transfusions which he received (CDC. West Nile virus infection in organ donor and transplant recipients---Georgia and Florida, 2002. MMWR 2002;51:790.). In another instance, a blood recipient in MS. Subsequently developed WNV encephalitis. Testing of 3/15 of her blood donors' retained specimens was positive for WNV RNA, in one case confirmed by culture (MMWR 9/20/02). Most recently, in a case investigation that is still in its preliminary stage, 2 patients who developed WNV encephalitis after receiving blood products were co-recipients of blood from a donor whose retained sample has tested positive for WNV RNA (joint CDC, FDA, State of Michigan Press Telebriefing, 9/27/02).
Based on an ongoing analysis of these and other case reports made to the Centers for Disease Control, it now appears highly likely that WNV can be transmitted by both organ transplantation and by blood transfusion. While the degree of risk is unknown at this time, and intensive investigation continues, the Public Health Service believes that all feasible steps should continue to be taken to reduce the risk. Because most patients with WNV viremia are likely to be asymptomatic, FDA is also working with the blood and medical diagnostics industry to encourage and facilitate the availability of a blood donor-screening test.
FDA Blood Safety Provisions
Donor Deferral
Blood establishments must defer donors not in good health. (See FDA regulations at 21 CFR 640.3.) The clinical course of WNV infection can range from asymptomatic, to mild symptoms suggestive of an acute infectious illness (i.e., fever, nausea, vomiting, flu-like symptoms), to, in less than 1% of those infected, severe neurological manifestations including meningoencephalitis, and rarely flaccid paralysis. Additional information concerning WNV can be obtained at the Center for Disease Control and Prevention website.
Careful attention to blood establishment's existing donor screening procedures should identify the approximately 20 percent of persons with WNV infection who are symptomatic. FDA wishes to emphasize the potential importance of these measures in reducing the theoretical risk of transfusion transmitted WNV, particularly in areas where human cases are occurring.
Component Quarantine and Retrieval
In cases of probable or proven recent West Nile Virus infection in a donor, discovered post-donation, or when the recipient of a transfusion is suspected or confirmed to have developed WNV infection following transfusion, Medical Directors of blood establishments should carefully evaluate the situation and consider product quarantine and retrieval.
Although no specific studies using West Nile virus have been performed, we believe that the risk of transmission by plasma derivatives is extremely low. WNV is a lipid-enveloped virus and is likely to be effectively inactivated by processes in place for these products, which have been shown to inactivate closely related flaviviruses.
FDA wishes to emphasize to patients and health care providers that when a blood transfusion is medically indicated, the benefits are currently believed to outweigh the risks of such a transfusion, including the risk of WNV infection. FDA is continuing to work with CDC and NIH to study this issue and is planning to issue further guidance on these matters in the very near future.
Development of Donor Screening Tests
FDA is interested in facilitating the development of commercial tests for detection of acute infection with WNV in blood and plasma donors, including the development of supplemental tests. FDA plans to sponsor a public scientific meeting on November 4-5, 2002 to discuss the development of these tests and the development of pathogen removal or inactivation methods to reduce the risk of WNV from blood transfusion.