Bacterial screening of apheresis platelets with a rapid test: a 113‐month single center experience

Platelet components and bacterial contamination: hospital perspective 2022

Bacterial contamination of platelet units has been one of the most common transfusion-transmitted infections. Approximately 4 to 7 fatalities are being reported to the US Food and Drug Administration (FDA) annually, which cites bacterially contaminated platelet units as the cause. Over the past 3 decades, different mitigation strategies have been introduced to minimize the risk of morbidity and mortality related to contaminated platelet units. The process of platelet collection and manufacturing as well as storage at 20°C to 24°C contributes to higher prevalence of contaminated units. The risk of transfusing bacterially contaminated platelets can be lowered using different types of interventions. Prevention of bacterial contamination can be done by strict adherence to techniques that minimize contamination during unit collection. The detection of bacteria in platelet products can be improved with a combination of rapid testing and bacterial cultures that involve large volume and delayed sampling. Finally, pathogen reduction can inactivate bacteria or other pathogens present in the unit. This article describes different strategies that blood centers and transfusion services have undertaken since October 2021 to meet FDA guidance requirements. Market forces as well as feasibility of different FDA-proposed approaches have limited the number of practical solutions to just a few. In addition, the blood product availability required hospitals to adopt more progressive strategies to provide patients with needed platelet products.

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.

Residual bacterial detection rates after primary culture as determined by secondary culture and rapid testing in platelet components: A systematic review and meta-analysis

BACKGROUND

Primary culture alone was a bacterial risk control strategy intended to facilitate interdiction of contaminated platelets (PLTs). A September 2019 FDA guidance includes secondary testing options to enhance safety. Our objective was to use meta-analysis to determine residual contamination risk after primary culture using secondary culture and rapid testing.

STUDY DESIGN AND METHODS

A December 2019 literature search identified articles on PLT bacterial detection rates using primary culture and a secondary testing method. We used meta-analysis to estimate secondary testing detection rates after a negative primary culture. We evaluated collection method, sample volume, sample time, and study date as potential sources of heterogeneity.

RESULTS

The search identified 6102 articles; 16 were included for meta-analysis. Of these, 12 used culture and five used rapid testing as a secondary testing method. Meta-analysis was based on a total of 103 968 components tested by secondary culture and 114 697 by rapid testing. The residual detection rate using secondary culture (DR_SC ) was 0.93 (95% CI, 0.24-0.6) per 1000 components, while residual detection rate using rapid testing (DR_RT ) was 0.09 (95% CI, 0.01-0.25) per 1000 components. Primary culture detection rate was the only statistically significant source of heterogeneity.

CONCLUSION

We evaluated bacterial detection rates after primary culture using rapid testing and secondary culture. These results provide a lower and upper bound on real-world residual clinical risk because these methods are designed to detect high-level exposures or any level of exposure, respectively. Rapid testing may miss some harmful exposures and secondary culture may identify some clinically insignificant exposures.

A national survey of hospital-based transfusion services on their approaches to platelet bacterial risk mitigation in response to the FDA final guidance for industry

BACKGROUND

Bacterial contamination of platelets is the leading infectious risk to the United States (US) blood supply. On 30 September 2019, the US Food and Drug Administration (FDA) published a Final Guidance for Industry to reduce the risk of transfusing platelets contaminated by bacteria. A national survey was undertaken to assess readiness, attitudes, and the potential impact on hospital-based transfusion services.

STUDY DESIGN AND METHODS

A survey was distributed to transfusion services in all 50 US states. Summary statistics were performed along with review and categorization of email feedback and free text comments.

RESULTS

Eighty-three transfusion services from 48 states participated in this survey study. Currently, the most common approach is primary culture performed at manufacturing (n = 49/83, 59%). Of the bacterial risk mitigation strategies provided by the FDA, the most frequently preferred are (a) pathogen reduced platelets (PRP) for up to 5-day storage (n = 36/77, 47%), (b) large volume delayed sampling (LVDS) ≥48 hours for up to 7-day storage (n = 16/77, 21%), and (c) primary culture ≥24 hours + secondary rapid testing for up to 7-day storage (n = 7/77, 9%). The main motivating factors for the survey participants' selected strategies to comply with FDA final guidance were product availability from supplier, reducing the risk of septic transfusion reactions (STR), and complexity of implementing and performing a new or additional test.

CONCLUSION

While having platelets to transfuse and preventing STR are of the utmost importance, nationwide, the majority of transfusion services do not want to take on performing new or additional testing in their laboratories.

How do you… decide which platelet bacterial risk mitigation strategy to select for your hospital-based transfusion service?

The United States Food and Drug Administration Final Guidance for Industry titled, "Bacterial Risk Control Strategies for Blood Collection Establishments and Transfusion Services to Enhance the Safety and Availability of Platelets for Transfusion" provides nine strategies for platelet bacterial risk mitigation. Even if it is assumed all strategies are comparable in terms of safety and efficacy, the decision of which to implement remains challenging. Some additional factors that warrant evaluation before selecting a strategy include the financial impact, process for implementation, logistics upon implementation, institutional acceptance by blood bank staff, administration and clinicians, and effect on platelet availability. To assist with this difficult choice, a panel of transfusion service physicians who have expertise on the topic and have already selected strategies for their transfusion services were recruited to provide varied perspectives. In addition, the use of a decision-making tool that objectively evaluates defined criteria for assessment of the nine strategies is described.