Predicting improvement in detection of bacteria in apheresis platelets by maintaining constant component sampling proportion.

BACKGROUND: In spite of interventions, approximately 1000 per 1,000,000 platelet (PLT) collections are contaminated with bacteria at collection. The current prestorage culture procedure at some blood centers is to inoculate a fixed volume from the collection bag (4-8 mL) regardless of collection volume. The sensitivity of early testing varies with the percent of collection volume sampled. We applied the Poisson model to determine whether sampling larger volumes might increase detection at pertinent contamination levels. STUDY DESIGN AND METHODS: The intervention was testing a fixed proportion of the collection volume from single, double, and triple collections. The Poisson model was applied to blood center data to calculate weighted average detection. Model 1 consisted of inoculating 3.2% of the collection volume from single, 1.6% from double, and 1.2% from triple PLT procedures (8 mL in each case). Model 2 consisted of inoculating 3.8% of the collection volume from all PLT procedures. Volume-related and non-volume-related contamination mechanisms were evaluated. RESULTS: Testing constant proportions of the collection volume (Model 2) increases percent detection over testing constant volumes (Model 1) (68% vs. 41% detection if contamination is 30 colony-forming units (CFUs)/collection bag and 17% vs. 9% detection if contamination is 5 CFUs/collection bag). At low levels of contamination (approx. 5 CFUs/bag), the intervention might double the number of contaminated units detected. CONCLUSION: Based on the application of the Poisson model to detection of bacteria in PLT concentrates, inoculating cultures with slightly consistent proportions of the collection volume should lead to a reduction in false negative tests and in the number of contaminated units transfused.

Two-year experience with aerobic culturing of apheresis and whole blood-derived platelets.

BACKGROUND: Throughout its system of regional centers, Blood Systems implemented culture based bacterial testing with a standardized protocol for both apheresis and whole blood-derived platelets (PLTs). STUDY DESIGN AND METHODS: After a 24-hour hold, 4 mL of PLT product was inoculated into an aerobic bottle (BacT/ALERT, bioMérieux). Cultures were incubated for 24 hours before routine product release to prevent distribution of infected products while minimizing consignee notification, product retrievals, and hospital PLT inventory problems. Initial-positives were further tested (and bacteria identified) by performing cultures from the original component and subcultures from the BacT/ALERT bottle. Results were categorized according to AABB recommended definitions with minor modifications. RESULTS: The rate of true-positive detections from culturing 122,971 apheresis PLTs was 0.017 percent (95% confidence interval [CI], 0.011%-0.026%). All true-positive microorganisms were Gram-positive with a predominance of coagulase-negative Staphylococcus and Bacillus species. Twenty of the 21 true-positive samples (95%) were detected by 24 hours but only 14 (68%) were detected by 18 hours. The false-positive rate due to contamination was 0.1 percent with the majority of isolates being skin or environmental organisms. Results did not differ significantly for whole blood-derived versus apheresis PLTs. CONCLUSION: These data corroborate the fact that the rate of detection of truly contaminated PLT apheresis products in the United States is approximately 1 in 5000 (0.02%); this is lower than the 0.03 to 0.05 percent rates that were generally quoted in the literature before the implementation of prospective bacterial culturing programs.

Safety and donor acceptance of an abbreviated donor history questionnaire.

BACKGROUND: Surveys have shown donor dissatisfaction with the duration of the donation process and repetitive questioning. An abbreviated donor history questionnaire (AQ) may improve satisfaction, but must be safe. STUDY DESIGN AND METHODS: An FDA-approved 34-question AQ was implemented in 2003. Travel, medication, and health history questions were decreased by 18. Donors were eligible for AQ if they had successfully completed three donor suitability assessments on the full-length questionnaire (FQ), including one in the prior 6 months. Data were analyzed from more than 50,000 donations during each of three 20-day periods over the first year of progressive implementation of the AQ. We evaluated the performance of the AQ by comparing donor deferrals for medical history (MHD), physical examination findings (PED), and reactive screening and/or confirmatory tests (RSCT) for viral markers among AQ-ineligible and AQ-eligible donors and separately among AQ-eligible donors who received AQ or FQ. RESULTS: Approximately one-third of presenting donors were AQ-eligible. Use of AQ progressed from 48 percent in October 2003 to 76 percent in November 2004. AQ-eligible donors had lower rates of MHD, PED, and RSCT than donors ineligible for AQ (p < 0.05). Among donors eligible for the AQ, those who received the FQ had slightly more MHD and PED than those who received the AQ (p < 0.05), but there was no difference in RSCT. A postdonation survey indicated significantly increased satisfaction and intent to donate among donors who received the AQ. CONCLUSIONS: In frequent repeat donors, use of an AQ led to increased donor satisfaction and no significant medical concerns about donor or recipient safety.

Triggers for switching from minipool testing by nucleic acid technology to individual-donation nucleic acid testing for West Nile virus: analysis of 2003 data to inform 2004 decision making.

BACKGROUND: Concern about West Nile virus (WNV) transfusion-transmitted infections missed by minipool (MP) nucleic acid testing (NAT) has prompted consideration of the use of individual-donation (ID) NAT. Strategies were investigated for the application of limited ID-NAT capacity in 2004. STUDY DESIGN AND METHODS: Patterns of WNV MP-NAT-reactive donations tested by the Blood Systems Laboratory each week for 79 blood centers from June 29 to November 23, 2003 (196 MP-NAT repeat-reactive [RR] donations among 801,697 units), were analyzed. ID-NAT initiation strategies were developed consisting of counts of RR donations and/or weekly RR rates, together with three ID-NAT discontinuation strategies, and ID testing burden was assessed based on these combined start and stop strategies. RESULTS: The effectiveness, reported as the percentage of MP-RR donations that would trigger ID-NAT based on each initiation strategy, ranged from 57 to 100 percent. The addition of a 1- or 2-week no-yield requirement for ID discontinuation substantially increased testing burden. Combined strategies resulted in projected ID-NAT of between 10 and 50 percent of donations for a 10- to 20-week period. For this organization, the most feasible ID-NAT initiation strategy was 2 MP-reactive donations and a weekly rate of 1 in 1000, which had an effectiveness of 81 percent and led to peak weekly ID-NAT of 20 to 25 percent of donations depending on the discontinuation rule. CONCLUSION: This new approach of targeted ID-NAT based on ongoing monitoring of MP-NAT yield may prove to be a rational policy for agents like WNV that cause seasonal and regional epidemics.