Bacterial screening of outdated buffy coat platelet pools using a culture system and a rapid immunoassay

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.

Adoption trends of point of issue Verax PGD rapid test for bacterial screening of platelets between 2013 and 2018 among hospitals supplied by the American Red Cross and impact on platelet availability

BACKGROUND

Point-of-issue tests, such as the Verax Pan Genera Detection (PGD) test, can be used to mitigate the occurrence of septic reactions. Little is known about how widespread the adoption of the PGD test is across US hospitals.

STUDY DESIGN/METHODS

The Red Cross hemovigilance database was used to determine the numbers of PGD-positive test results between 2013 and 2018. An examination of the impact of a reactive PGD test on product availability was performed for 2018.

RESULTS

The number of reported cases doubled, rising from approximately 50 to 100 per year between 2013 and 2018. A total of 475 initially reactive PGD tests during the entire study period were reported, and 7 (1.5%) of these were determined to be true positives. Hospitals surveyed reported testing platelet units once, with no repeat testing if the unit was PGD reactive. Evaluation of the reported PGD reactive cases for apheresis platelets for 2018 (n = 93) resulted in an estimated cost to the blood center of $87,000, which included the labor and material costs of working up the cases and the estimated value of the lost 64 units and co-components. In addition, there was a loss of the opportunity to collect over 85 apheresis platelets during the time the implicated donor was temporarily deferred.

CONCLUSIONS

The number of hospital reports of reactive PGD tests has shown modest growth in the past 5 years. The number of initially reactive PGD tests that were confirmed was minimal. Blood centers can incur cost and platelet inventory loss from initially false-positive test results.

A dual-center evaluation of platelet culture vials to detect the presence of microorganisms in platelets

BACKGROUND

Microorganism contamination of platelets results in a high risk of transfusion-related sepsis. Here, the ability of culture vials (BD BACTEC Platelet Aerobic/F and Platelet Anaerobic/F vials, Becton, Dickinson and Company) to detect microorganisms in leukoreduced apheresis platelets (LRAPs) and leukoreduced whole blood platelet concentrates (LRWBPCs) was assessed.

METHODS

LRAPs or LRWBPCs were inoculated into Aerobic/F and Anaerobic/F vials and placed in a blood culturing system (BD BACTEC FX System, Becton, Dickinson and Company) for growth/monitoring over 7 days to detect preexisting contamination during false-positive testing. Subsequently, platelets were seeded with microorganisms at approximately 10 CFU/mL or approximately 1 CFU/mL to simulate contamination. Aerobic/F and Anaerobic/F vials were inoculated with platelets (sets of 12). Microorganism growth was detected in the BACTEC FX instrument over 7 days. Overall, 2925 vials were tested.

RESULTS

Of the 1905 vials included in the microorganism detection phase, 63 (3.3%) Aerobic/F and 16 (0.8%) Anaerobic/F vials were both BACTEC FX and subculture negative. From the remaining 1827 vials, two (0.1%) Anaerobic/F vials were false positive; no false positives were observed in Aerobic/F vials, and no false negatives occurred in either vial type. Of the remaining 1825 vials (99.9%), 955 Aerobic/F and 870 Anaerobic/F vials were true positives. The mean-time-to-detection range was 8.5 to 77 hours. All true-positive Aerobic/F and Anaerobic/F vials showed 100% agreement with subculture for positive identification of seeded microorganisms.

CONCLUSION

Aerobic/F and Anaerobic/F vials facilitate contamination detection in LRAPs and LRWBPCs down to approximately 1 CFU/mL. These results support the use of Aerobic/F and Anaerobic/F vials for quality control testing of platelets before transfusion.

Refrigeration, cryopreservation and pathogen inactivation: an updated perspective on platelet storage conditions

Conventional storage of platelet concentrates limits their shelf life to between 5 and 7 days due to the risk of bacterial proliferation and the development of the platelet storage lesion. Cold storage and cryopreservation of platelets may facilitate extension of the shelf life to weeks and years, and may also provide the benefit of being more haemostatically effective than conventionally stored platelets. Further, treatment of platelet concentrates with pathogen inactivation systems reduces bacterial contamination and provides a safeguard against the risk of emerging and re-emerging pathogens. While each of these alternative storage techniques is gaining traction individually, little work has been done to examine the effect of combining treatments in an effort to further improve product safety and minimize wastage. This review aims to discuss the benefits of alternative storage techniques and how they may be combined to alleviate the problems associated with conventional platelet storage.

Noninvasive pH monitoring for bacterial detection in platelet concentrates

BACKGROUND

Bacterial contamination of platelet concentrates (PCs) remains the prevalent posttransfusion infectious risk. The pH SAFE system, a noninvasive method used to measure pH of PC for quality control, was evaluated herein as a rapid method to detect bacterial contamination in PCs.

STUDY DESIGN AND METHODS

Pairs of ABO-D-matched apheresis and buffy coat PCs were pooled and split into two pH SAFE platelet bags. One of the bags served as the control unit, while the other was inoculated with one of nine clinically relevant bacteria (target concentration approx. 1 colony-forming units [CFUs]/mL). The pH of both PCs was measured over 7 days of storage at approximately 4-hour intervals during daytime. One-milliliter samples were taken at the testing points to determine bacterial concentration.

RESULTS

PCs with pH values of less than 6.6 or with a pH change over time (ΔpH/Δtime) greater or equal than 0.046 pH units/hr are suspected of being contaminated. pH decreased significantly during storage in all bacterially inoculated PC at concentrations of more than 10(7) CFUs/mL (p < 0.0001). A significant decrease in pH (p < 0.0001) was noticed as early as 28 hours in units with Bacillus cereus and as late as 125 hours in units containing Staphylococcus epidermidis. Interestingly, PCs containing Gram-negative species showed a decline in pH followed by a rebound.

CONCLUSIONS

The pH SAFE system allows for repeated, noninvasive pH screening during PC storage. A significant decrease in pH could serve as an indicator of clinically significant levels of bacterial contamination. Since differences in pH decline were observed among bacterial species, continuous pH monitoring in PCs is recommended.

Characterization of the growth dynamics and biofilm formation of Staphylococcus epidermidis strains isolated from contaminated platelet units

Bacterial contamination of platelet concentrates (PCs) poses the highest transfusion-associated infectious risk, with Staphylococcus epidermidis being a predominant contaminant. Herein, the growth dynamics of 20 S. epidermidis strains in PCs and regular media were characterized. Strains were categorized as fast (short lag phase) or slow (long lag phase) growers in PCs. All strains were evaluated for the presence of the biofilm-associated icaAD genes by PCR, their capability to produce extracellular polysaccharide (slime) on Congo red agar plates and their ability to form surface-attached aggregates (biofilms) in glucose-supplemented trypticase soy broth (TSBg) using a crystal violet staining assay. A subset of four strains (two slow growers and two fast growers) was further examined for the ability for biofilm formation in PCs. Two of these strains carried the icAD genes, formed slime and produced biofilms in TSBg and PCs, while the other two strains, which did not carry icaAD, did not produce slime or form biofilms in TSBg. Although the two ica-negative slime-negative strains did not form biofilms in media, they displayed a biofilm-positive phenotype in PCs. Although all four strains formed biofilms in PCs, the two slow growers formed significantly more biofilms than the fast growers. Furthermore, growth experiments of the two ica-positive strains in plasma-conditioned platelet bags containing TSBg revealed that a slow grower isolate was more likely to escape culture-based screening than a fast grower strain. Therefore, this study provides novel evidence that links S. epidermidis biofilm formation with slow growth in PCs and suggests that slow-growing biofilm-positive S. epidermidis would be more likely to be missed with automate culture.

Diagnostic methods for platelet bacteria screening: current status and developments

Bacterial contamination of blood components and the prevention of transfusion-associated bacterial infection still remains a major challenge in transfusion medicine. Over the past few decades, a significant reduction in the transmission of viral infections has been achieved due to the introduction of mandatory virus screening. Platelet concentrates (PCs) represent one of the highest risks for bacterial infection. This is due to the required storage conditions for PCs in gas-permeable containers at room temperature with constant agitation, which support bacterial proliferation from low contamination levels to high titers. In contrast to virus screening, since 1997 in Germany bacterial testing of PCs is only performed as a routine quality control or, since 2008, to prolong the shelf life to 5 days. In general, bacterial screening of PCs by cultivation methods is implemented by the various blood services. Although these culturing systems will remain the gold standard, the significance of rapid methods for screening for bacterial contamination has increased over the last few years. These new methods provide powerful tools for increasing the bacterial safety of blood components. This article summarizes the course of policies and provisions introduced to increase bacterial safety of blood components in Germany. Furthermore, we give an overview of the different diagnostic methods for bacterial screening of PCs and their current applicability in routine screening processes.