West Nile Virus Transmission via Organ Transplantation and Blood Transfusion — Louisiana, 2008

Editorial Note

This report describes two cases of probable transfusion-transmitted WNV from a common blood donor. One infection resulted in WNND via an organ donor, and the other resulted in asymptomatic WNV infection via blood transfusion directly. The source of infection cannot be proved definitively because blood samples or other components from the implicated donation were unavailable for testing. However, evidence of WNV infection in the two patients linked to blood products from a common donor, along with serologic evidence of recent infection and a febrile illness in the donor shortly after blood donation, make these probable cases of transfusion-transmitted WNV.^[4]

After heart transplantation, the organ recipient described in this report was immunosuppressed when he had onset of WNND. This patient likely was infected with WNV after receipt of the transplant heart from a donor who received multiple blood transfusions, at least one of which was suspected to contain WNV. If exposed to WNV, transplant recipients are at high risk for WNND; however, organ donors are not routinely screened for WNV. Both organ donors and transplant recipients often receive multiple transfusions. Early recognition and notification of a potential donor-related transmitted disease could result in earlier WNV infection diagnosis and initiation of supportive care in organ transplant recipients who received organs from the same donor. Health-care providers should consider WNND when neurologic complications occur in patients after transfusion or organ transplantation. In addition, timely recognition of potential contamination with WNV or other transfusion-transmitted pathogens could lead to removal of potentially infectious blood products from the blood supply.

Screening blood or organ and tissue donors based on clinical symptoms is ineffective at preventing donor-related WNV infections.^[5] The Food and Drug Administration (FDA) provides guidance to blood centers for donor screening to reduce the risk for transfusion-transmitted disease. FDA recommends screening year-round for WNV using a licensed NAT (MP-NAT or ID-NAT) on donor samples of whole blood and blood components.^[6] Because of the dilution effect inherent in screening by MP-NAT, this method is less sensitive than ID-NAT. FDA further recommends that blood centers using MP-NAT screening establish criteria to switch to ID-NAT during periods of high WNV activity in their geographic area of collection. No cases of transfusion-related transmission have been reported when using ID-NAT to screen for WNV. However, routine ID-NAT screening is not feasible for many blood centers because of the resulting logistic and financial burdens. Therefore, most blood centers use WNV MP-NAT screening until a trigger threshold of one or more positive MP-NAT results is reached over a specific period and then switch to ID-NAT. Each blood center has its own triggering threshold, developed within the constraints of FDA guidance and standards of AABB (formerly known as the American Association of Blood Banks).^{[7] ¶}

The WNV screening policy at the laboratory used by blood center A, where the presumed WNV-contaminated donation was collected, set the trigger to switch from MP-NAT to ID-NAT as identification of two MP-NAT positive donations from the same postal code area within a 7-day period. Blood center A had collected an MP-NAT–positive donation on September 11, and collected the implicated blood donation on September 15. Blood center B, another blood center collecting in the same region, had a policy of transitioning from MP-NAT to ID-NAT after identification of one MP-NAT positive donation within its blood collection area, including those identified by other blood centers in the region. Screening data from September indicated that blood center B transitioned to ID-NAT during the period the implicated donation was collected by blood center A, based on the positive MP-NAT collected on September 11 by another blood center, which collects blood in a region that overlaps that of blood center A. Use of triggering criteria, at a minimum, as sensitive as that used by blood center B could have resulted in the implicated donation being tested by ID-NAT, found reactive, and removed from the blood supply.

Adoption of a single standard for all triggering criteria would be desirable; however, differences exist between blood centers because of geographic variability of WNV activity, amplifying logistical concerns. Although universal ID-NAT screening is the more conservative option, MP-NAT can be a highly effective screening strategy if coupled with an appropriate strategy for triggering ID-NAT testing. Recent modeling has suggested that initiation of ID-NAT in a previously defined geographic region or zone should be based on one MP-NAT–reactive donation.^[8] A second model examining 27 triggering strategies suggested that effectiveness increased when triggering was based on one positive MP-NAT rather than two during a 7-day period.^[9] Further simulations based on data from a 2006 transfusion-transmitted WNV investigation, in which the positive donation went undetected by minipool testing,^[10] suggest that triggering based on one MP-NAT might have resulted in detection of the WNV positive unit (CDC, unpublished data, 2008). Similarly, the triggering data described in this report suggest that the WNV-contaminated donation might have been detected before use by triggering to ID-NAT on one MP-NAT positive donation. In regions served by more than one blood center, close communication between blood centers locally is critical. Blood centers can increase the likelihood of detecting WNV in donated blood by using screening strategies that trigger the most timely use of ID-NAT, selection of geographic areas larger than a single postal code area, and ongoing communication of screening results between all facilities that collect blood in a geographic area.

Morbidity and Mortality Weekly Report. 2009;58(45):1263-1267. © 2009  Centers for Disease Control and Prevention (CDC)