The Development of West Nile Virus Safety Policies by Canadian Blood Services: Guiding Principles and a Comparison Between Canada and the United States
Section snippets
Blood Safety Policies Implemented Before the 2003 WNV Season
In early November 2002, the US Food and Drug Administration convened a workshop on the development of blood donor screening assays for WNV. The workshop concluded with a clear message that industry should develop and blood collection agencies should implement a screening test for WNV RNA (ie, a nucleic acid amplification test [NAT] in a minipool [MP] format) before the 2003 mosquito season.11 A target was set to screen all blood donations for WNV RNA by July 1, 2003.
In mid-December 2002, the
Modifications of Policy During the Summer of 2003
In late August 2003, the American Red Cross began individual-donation (ID) nucleic acid amplification testing in 2 states with unusually high WNV disease activity.15 This was based on the observation that breakthrough WNV infections had been observed after transfusion of MP NAT–negative units and that retrospective testing of donations by ID NAT in some of these cases was able to detect an infectious donor with a low level of viremia.16, 17
In Canada, the WNV epidemic peaked in August 2003 and
2004 Contingency Planning: Targeted ID Nucleic Acid Amplification Testing and Other Measures
United States data from the 2003 transmission season indicated that 6 cases of transfusion-transmitted WNV infection occurred from WNV MP NAT–negative blood components that contained very low levels of virus and were IgM-negative.21 Furthermore, it was estimated that if ID nucleic acid amplification testing were implemented early in a region with a severe epidemic, 5% to 10% of the units detected would be MP NAT–negative, ID NAT–positive, IgM-negative, and therefore potentially infectious.17, 19
Implementation of Policies in 2004
Canadian Blood Services initiated targeted ID NAT on August 2, 2004. At that time, there were no MP NAT–positive donors and no human WNV cases in Canada. Thus, CBS initially targeted ID NAT to donations from public health regions where avian WNV activity had been detected. With the reporting of a human case in a public health region in Ontario in the week of August 9, CBS redirected some of its ID-NAT capacity to collections from that public health region. Because additional cases were reported
2005 Contingency Planning
For 2005, CBS adopted an approach to ID nucleic acid amplification testing that was very similar to the one in the United States in that it used specific triggers for introducing ID nucleic acid amplification testing of donors from a particular area. More specifically, in 2005, CBS intended to begin ID nucleic acid amplification testing of donations made in a particular public health region when 1 positive donor was identified by MP nucleic acid amplification testing in that region. Héma-Québec
Implementation of Policies in 2005
Canadian Blood Services initiated targeted ID NAT on July 27, 2005, after an MP NAT–positive donation was detected in the Ottawa public health region on July 26, 2005. Between July 26 and August 22, 2005, 13 positive donations were made in Ontario (7), Manitoba (3), Saskatchewan (2), and Alberta (1). One more positive donation was made on August 31 in Montreal and was reported by Héma-Québec. Thus, by the first week of September, the same number of positive donations as had been made in Canada
Summary of Results: 2002-2005
After detailed investigation, 4 probable or possible cases of transfusion-transmitted WNV were documented in 2002.10 None were identified in 2003 or 2004 or have hitherto been reported in 2005 (Table 3). Systemwide MP-NAT screening was begun on July 2, 2003. This testing identified 12 WNV RNA–positive units from July 22 to August 31, 2003. An additional 2 U positive only by ID NAT were detected on September 2, 2003, in Saskatchewan where ID nucleic acid amplification testing was conducted for 3
Application of the Precautionary Principle
The goal of achieving incremental safety (even if small) guided all CBS decisions. The only competing factors were unacceptable impact on blood availability and insurmountable logistic or financial limitations (eg, computer system restrictions, lack of assay automation). When attempting to assess the potential risk for WNV of recipients and when there were unknown factors such as the timing and extent of the next year's epidemic, the worst-case scenario was used to determine the interventions
Discussion
As seen in Table 1, most CBS policy decisions have been similar to those implemented in the United States. However, several CBS policies were more stringent, especially those adopted in mid-2003. These included early partial implementation of an in-house–developed WNV RNA assay, the stockpiling of frozen plasma products in the winter for transfusion in WNV-affected areas in the summer, a special recruitment campaign for red blood cell collections before the start of the WNV season, and an
Acknowledgments
The authors thank Drs Susan Stramer and Ted Alport for their review of the manuscript and the members of the CBS WNV Steering Committee for their input in policy development, with special thanks to Ms Edna Zuber, Mr Vito Scalia, Mr Tom Walker, and Mr David Howe.
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