The comparative safety of bacterial risk control strategies for platelet components: a simulation study

Changing Strategies for the Detection of Bacteria in Platelet Components in Ireland: From Primary and Secondary Culture (2010-2020) to Large Volume Delayed Sampling (2020-2023)

Bacterial contamination of platelet components (PC) poses the greatest microbial risk to recipients, as bacteria can multiply over the course of PC storage at room temperature. Between 2010 and 2020, the Irish Blood Transfusion Service (IBTS) screened over 170,000 buffy coat-derived pooled (BCDP) and single-donor apheresis platelets (SDAPs) with the BACT/ALERT 3D microbial detection system (Biomerieux, L'Etoile, France), using a two-step screening protocol which incorporated primary and secondary cultures. Although the protocol was successful in averting septic transfusion reactions (STRs), testing large sample volumes at later time points was reported to improve detection of bacterial contamination. A modified large-volume delayed sampling (LVDS)-type protocol was adopted in 2020, which in the case of SDAP was applied to collections rather than individual splits (2020-2023, 44,642 PC screened). Rates of bacterial contamination for BCDP were 0.125% on Day-2, 0.043% on Day-4 vs. 0.191% in the post-LVDS period. SDAP contamination rates in the pre-LVDS period were 0.065% on Day-1, 0.017% on Day-4 vs. 0.072% in the post-LVDS period. Confirmed STRs were absent, and the interdiction rate for possibly contaminated SDAP was over 70%. In the post-LVDS period, BCDPs had a higher total positivity rate than SDAPs, 0.191% (1:525) versus 0.072% (1:1385), respectively, (chi-squared 12.124, 1 df, p = 0.0005). The majority of organisms detected were skin-flora-type, low pathogenicity organisms, including coagulase-negative staphylococci and Cutibacterium acnes, with little change in the frequency of clinically significant organisms identified over time. Both protocols prevented the issue of potentially harmful components contaminated (rarely) with a range of pathogenic bacteria, including Escherichia coli, Serratia marcesens, Staphylococcus aureus, and streptococci. Culture positivity of outdates post-LVDS whereby 100% of expired platelets are retested provides a residual risk estimate of 0.06% (95% CI 0.016-0.150). However, bacterial contamination rates in expired platelets did not demonstrate a statistically significant difference between the pre-LVDS 0.100% (CI 0.033-0.234) and post-LVDS 0.059% (0.016-0.150) periods (chi-squared = 0.651, 1 df, p = 0.42).

Meta-analysis of bacterial growth characteristics in platelet components: Refining the inputs of a simulation analysis comparing the relative safety of testing strategies

BACKGROUND

The relative safety of bacterial risk control strategies for platelets that include culture with or without rapid testing has been compared using simulation analysis. A wide range of bacterial lag and doubling times were included. However, published data on growth rates are available and these data have not been synthesized. We conducted a systematic review and meta-analysis to estimate growth rates and used these estimates to refine a comparative safety analysis of bacterial risk control strategies in the FDA guidance STUDY DESIGN AND METHODS: Data were extracted from published studies on bacterial growth rates in platelet components during storage. These data were used to estimate the practical range of growth rates. This refined the inputs for a simulation model comparing the safety of the testing strategies.

RESULTS

In total, 108 growth curves for 11 different aerobic organisms were obtained. Doubling times ranged from 0.8 to 12 h, but the lower 90% range was approximately 1-5 h. The revised comparative safety simulation using the narrower 1-5-h range showed similar rankings to the prior simulation, with 48-h large-volume delayed sampling with 7-day expiration (48C-7) demonstrating the lowest-ranking relative performance at the 103 and 105 colony forming unit (CFU)/mL exposure thresholds.

DISCUSSION

This was a two-step study. First, meta-analysis of published data on aerobic bacterial growth rates in stored platelets showed the vast majority of doubling times were 1-5 h. Next, an updated comparative safety simulation yielded similar results to a prior study, with 48C-7 showing the least favorable relative safety performance.

Application of Standardized Residual Component Culture Criteria for Suspected Septic Transfusion Reactions Would Increase the Component Culturing Rate at a Single Academic Medical Center

OBJECTIVES

The 2019 SCARED study developed the Biomedical Excellence for Safer Transfusion (BEST) criteria in an effort to standardize the decision to culture residual units in the context of suspected septic transfusion reactions (STRs). The goal of this study was to apply the BEST criteria to determine the effect on the transfusion reaction decision to culture.

METHODS

This retrospective, single-center, cross-sectional study assessed adult transfusion reactions identified in calendar years 2013 to 2020. Reactions following transfusion of RBCs, platelets, and plasma were included, and the decisions to culture following strict application of BEST criteria were compared with decisions to culture in actual practice.

RESULTS

In total, 1,068 transfusion reactions were reported and 200 (19%) suspected STRs were cultured, all with negative results; 303 (28%) reactions would have been cultured per strict application of the BEST criteria. Concordance between actual culture decision and BEST criteria recommendation was 62% for cultured components and 79% for components that were not cultured.

CONCLUSIONS

BEST criteria provide objective recommendations of when to culture residual units implicated in suspected STRs, but strict application of these criteria may result in increased culture rates. Clinical correlation to aid in the decision to culture is recommended.

The international experience of bacterial screen testing of platelet components with automated microbial detection systems: An update

In 2014, the bacterial subgroup of the Transfusion-Transmitted Infectious Diseases working party of ISBT published a review on the International Experience of Bacterial Screen Testing of Platelet Components (PCs) with an Automated Microbial Detection System. The purpose of this review, which is focused on publications on or after 2014, is to summarize recent experiences related to bacterial contamination of PCs and the use of an automated culture method to safeguard the blood supply. We first reviewed septic transfusion reactions after PC transfusion as reported in national haemovigilance systems along with a few reports from various countries on bacterial contamination of blood products. Next, we reviewed PC automated culture protocols employed by national blood services in the United Kingdom, Australia, Canada and large blood collection organization and hospital transfusion services in the United States. Then, we acknowledged the limitations of currently available culture methodologies in abating the risks of transfusion-transmitted bacterial infection, through a review of case reports. This review was neither meant to be critical of the literature reviewed nor meant to identify or recommend a best practice. We concluded that significant risk reduction can be achieved by one or a combination of more than one strategy. No one approach is feasible for all institutions worldwide. In selecting strategies, institutions should consider the possible impact on platelet components availability and entertain a risk-based decision-making approach that accounts for operational, logistical and financial factors.

The 4-Year Experience with Implementation and Routine Use of Pathogen Reduction in a Brazilian Hospital

(1) Background: We reviewed the logistics of the implementation of pathogen reduction (PR) using the INTERCEPT Blood System™ for platelets and the experience with routine use and clinical outcomes in the patient population at the Sírio-Libanês Hospital of São Paulo, Brazil. (2) Methods: Platelet concentrate (PC), including pathogen reduced (PR-PC) production, inventory management, discard rates, blood utilization, and clinical outcomes were analyzed over the 40 months before and after PR implementation. Age distribution and wastage rates were compared over the 10 months before and after approval for PR-PC to be stored for up to seven days. (3) Results: A 100% PR-PC inventory was achieved by increasing double apheresis collections and production of double doses using pools of two single apheresis units. Discard rates decreased from 6% to 3% after PR implementation and further decreased to 1.2% after seven-day storage extension for PR-PCs. The blood utilization remained stable, with no increase in component utilization. A significant decrease in adverse transfusion events was observed after the PR implementation. (4) Conclusion: Our experience demonstrates the feasibility for Brazilian blood centers to achieve a 100% PR-PC inventory. All patients at our hospital received PR-PC and showed no increase in blood component utilization and decreased rates of adverse transfusion reactions.

Platelet Component False Positive Detection Rate in Aerobic and Anaerobic Primary Culture: A Systematic Review and Meta-Analysis

Septic reactions from platelet transfusions are one of the leading causes of transfusion-associated mortality. The FDA guidance for platelet bacterial risk control includes bacterial culture using both aerobic and anaerobic bottles. Several studies have reported false positive rates (FPR) of culture, but these data have not been summarized or influencing factors analyzed. A systematic review and meta-analysis was performed according to published guidelines to assess the false positive rate and influencing factors. Eighteen studies were included for analysis. The combined aerobic/anaerobic FPR was 2.4 events per thousand (EPT) with a prediction interval of 0.5 to 5.7, while the aerobic FPR rate was 1.0 EPT (prediction interval: 0.2-2.2) and the anaerobic rate was 1.8 EPT. Estimates were based on a total of almost 5 million units tested. The rate of false positives due to instrument error was between 0.5-1.7 EPT, while it was between 0.3-1.0 EPT for sampling contamination based on whether only aerobic, anaerobic, or aerobic/anaerobic cultures were performed. The FPR is approximately 2 to 5 times higher than the literature reported true positive rate of 0.5 EPT.

The impact of the sample time of secondary bacterial culture on the risk of exposure to contaminated platelet components: A mathematical analysis

BACKGROUND

The US Food and Drug Administration (FDA) issued a guidance for bacterial risk control strategies for platelet components in September 2019 that includes strategies using secondary bacterial culture (SBC). While an SBC likely increases safety, the optimal timing of the SBC is unknown. Our aim was to develop a model to provide insight into the best time for SBC sampling.

STUDY DESIGN AND METHODS

We developed a mathematical model based on the conditional probability of a bacterial contamination event. The model evaluates the impact of secondary culture sampling time over a range of bacterial contamination scenarios (lag and doubling times), with the primary outcome being the optimal secondary sampling time and the associated risk.

RESULTS

Residual risk of exposure decreased with increasing inoculum size, later sampling times for primary culture, and using higher thresholds of exposure (in colony-forming units per milliliter). Given a level of exposure, the optimal sampling time for secondary culture depended on the timing of primary culture and on the expiration time. In general, the optimal sampling time for secondary culture was approximately halfway between the time of primary culture and the expiration time.

CONCLUSION

Our model supports that the FDA guidance is quite reasonable and that sampling earlier in the specified secondary culture windows may be most optimal for safety.