Bacterial screening of platelet concentrates: results of 2 years active surveillance of transfused positive cultured units released as negative to date

Current status of rapid bacterial detection methods for platelet components: A 20-year review by the ISBT Transfusion-Transmitted Infectious Diseases Working Party Subgroup on Bacteria

BACKGROUND AND OBJECTIVES

Bacterial contamination of platelet components (PCs) poses a safety challenge for transfusion patients. Despite mitigation interventions, the residual risk of transfusion-transmitted bacterial infections remains predominant. PC safety can be improved either by pathogen reduction or by implementation of bacterial detection methods. Detection methodologies include culture methods and rapid detection methods. The current review focuses on currently available rapid detection methods.

MATERIALS AND METHODS

We reviewed published manuscripts since 2000 on rapid bacterial detection methods used for PC screening with result determination within 4 h. Methods meeting this criterion included Verax PGDprime, BacTx and nucleic amplification testing. The analytical and diagnostic sensitivity and specificity of these systems were assessed.

RESULTS

The analytical sensitivity between the different detection methods ranged between 50 and 100,000 CFU/ml. The sample volume used by these testing systems varies between 0.5 and 1.0 ml of PCs. A delay of at least 48 h before sampling enhances detectability. All rapid detection methods generate results in a timely manner, allowing testing to be performed before transfusion with optimal sensitivity.

CONCLUSION

Rapid detection methods improve PC safety regarding bacterial contamination. The assays are optimal for rapidly growing bacteria, which are more likely to cause septic transfusion reactions in patients. Because of the reduced diagnostic sensitivity, the sample collection should be late in shelf-life and ideally just before transfusion. The major benefit of these methods is that the test result can be obtained before releasing PCs for transfusion or to be used in combination with other screening methods applied early during PC storage.

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.

Bacterial contamination rate of platelet components by primary culture: a systematic review and meta-analysis

BACKGROUND

Platelets have the highest bacterial contamination risk of all blood components, and septic transfusion reactions remain a problem. A good estimate of contamination rates could provide information about residual risk and inform optimal testing strategies. We performed a systematic review and meta-analysis of platelet contamination rates by primary culture.

STUDY DESIGN AND METHODS

A literature search in December 2019 identified articles on platelet contamination rates using primary culture. We used meta-analysis to estimate the overall rate of contamination and meta-regression to identify heterogeneity. We studied the following sources of heterogeneity: collection method, sample volume, positivity criteria, and study date. Contamination rate estimates were obtained for apheresis (AP), platelet rich plasma (PRP), and buffy coat (BC) collection methods.

RESULTS

The search identified 6102 studies, and 22 were included for meta-analysis. Among these 22 studies, there were 21 AP cohorts (4,072,022 components), 4 PRP cohorts (138,869 components), and 15 BC cohorts (1,474,679 components). The overall mean contamination rate per 1000 components was 0.51 (95% CI: 0.38-0.67) including AP (0.23, 95% CI: 0.18-0.28), PRP, (0.38, 95% CI: 0.15-0.70), and BC (1.12, 95% CI: 0.51-1.96). There was considerable variability within each collection method. Sample volume, positivity criteria, and publication year were significant sources of heterogeneity.

CONCLUSION

The bacterial contamination rate of platelets by primary culture is 1 in 1961. AP and PRP components showed a lower contamination rate than BC components. There is clinically significant between-study variability for each method. Larger sample volumes increased sensitivity, and bacterial contamination rates have decreased over time.

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.

Storage time of platelet concentrates and risk of a positive blood culture: a nationwide cohort study

BACKGROUND

Concern of transfusion-transmitted bacterial infections has been the major hurdle to extend shelf life of platelet (PLT) concentrates. We aimed to investigate the association between storage time and risk of positive blood cultures at different times after transfusion.

STUDY DESIGN AND METHODS

We performed a nationwide cohort study among PLT transfusion recipients in Denmark between 2010 and 2012, as recorded in the Scandinavian Donations and Transfusions (SCANDAT2) database. Linking with a nationwide database on blood cultures (MiBa), we compared the incidence of a positive blood culture among recipients of PLTs stored 6 to 7 days (old) to those receiving fresh PLTs (1-5 days), using Poisson regression models. We considered cumulative exposures in windows of 1, 3, 5, and 7 days.

RESULTS

A total of 9776 patients received 66,101 PLT transfusions. The incidence rate ratio (IRR) of a positive blood culture the day after transfusion of at least one old PLT concentrate was 0.77 (95% confidence interval [CI], 0.54-1.09) compared to transfusion of fresh PLT concentrates. The incidence rate of a positive blood culture was lower the day after receiving one old compared to one fresh PLT concentrate (IRR, 0.57; 95% CI, 0.37-0.87). Three, 5, or 7 days after transfusion, storage time was not associated with the risk of a positive blood culture.

CONCLUSION

Storage of buffy coat-derived PLT concentrates in PAS-C up to 7 days seems safe regarding the risk of a positive blood culture. If anything, transfusion of a single old PLT concentrate may decrease this risk the following day.

Bacterial screening of platelet components by National Health Service Blood and Transplant, an effective risk reduction measure

BACKGROUND

Bacterial contamination of blood components remains a major cause of sepsis in transfusion medicine. Between 2006 and 2010 in the 5 years before the introduction of bacterial screening of platelet (PLT) components by National Health Service Blood and Transplant (NHSBT), seven cases of PLT component-associated transmission of bacterial infection were recorded for 10 patients, three of which were fatal.

STUDY DESIGN AND METHODS

Sampling of individual PLT components was undertaken at 36 to 48 hours after donation and tested in the BacT/ALERT system with 8 mL inoculated into each of aerobic and anaerobic culture bottles. Bottles were incubated until the end of the 7-day shelf life and initial reactive bottles were examined for contamination. Bacterial screened time-expired PLTs were tested as in the screen method.

RESULTS

From February 2011 to September 2015, a total of 1,239,029 PLT components were screened. Initial-reactive, confirmed-positive, and false-positive rates were 0.37, 0.03, and 0.19%, respectively. False-negative cultures, all with Staphylococcus aureus, occurred on four occasions; three were visually detected before transfusion and one confirmed transmission resulted in patient morbidity. The NHSBT screening protocol effectively reduced the number of clinically adverse transfusion transmissions by 90% in this reporting period, compared to a similar time period before implementation. Delayed testing of 4515 time-expired PLT units after screening revealed no positives.

CONCLUSION

The implementation of bacterial screening of PLT components with the NHSBT BacT/ALERT protocol was an effective risk reduction measure and increased the safety of the blood supply.

A study protocol for a randomised controlled trial evaluating clinical effects of platelet transfusion products: the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) trial

INTRODUCTION

Patients with chemotherapy-induced thrombocytopaenia frequently experience minor and sometimes severe bleeding complications. Unrestrictive availability of safe and effective blood products is presumed by treating physicians as well as patients. Pathogen reduction technology potentially offers the opportunity to enhance safety by reducing bacterial and viral contamination of platelet products along with a potential reduction of alloimmunisation in patients receiving multiple platelet transfusions.

METHODS AND ANALYSIS

To test efficacy, a randomised, single-blinded, multicentre controlled trial was designed to evaluate clinical non-inferiority of pathogen-reduced platelet concentrates treated by the Mirasol system, compared with standard plasma-stored platelet concentrates using the percentage of patients with WHO grade ≥ 2 bleeding complications as the primary endpoint. The upper limit of the 95% CI of the non-inferiority margin was chosen to be a ≤ 12.5% increase in this percentage. Bleeding symptoms are actively monitored on a daily basis. The adjudication of the bleeding grade is performed by 3 adjudicators, blinded to the platelet product randomisation as well as by an automated computer algorithm. Interim analyses evaluating bleeding complications as well as serious adverse events are performed after each batch of 60 patients. The study started in 2010 and patients will be enrolled up to a maximum of 618 patients, depending on the results of consecutive interim analyses. A flexible stopping rule was designed allowing stopping for non-inferiority or futility. Besides analysing effects of pathogen reduction on clinical efficacy, the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) is designed to answer several other pending questions and translational issues related to bleeding and alloimmunisation, formulated as secondary and tertiary endpoints.

ETHICS AND DISSEMINATION

Ethics approval was obtained in all 3 participating countries. Results of the main trial and each of the secondary endpoints will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NTR2106; Pre-results.

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.

Evaluation of an ethidium monoazide-enhanced 16S rDNA real-time polymerase chain reaction assay for bacterial screening of platelet concentrates and comparison with automated culture

BACKGROUND

Culture-based systems are currently the preferred means for bacterial screening of platelet (PLT) concentrates. Alternative bacterial detection techniques based on nucleic acid amplification have also been developed but these have yet to be fully evaluated. In this study we evaluate a novel 16S rDNA polymerase chain reaction (PCR) assay and compare its performance with automated culture.

STUDY DESIGN AND METHODS

A total of 2050 time-expired, 176 fresh, and 400 initial-reactive PLT packs were tested by real-time PCR using broadly reactive 16S primers and a "universal" probe (TaqMan, Invitrogen). PLTs were also tested using a microbial detection system (BacT/ALERT, bioMérieux) under aerobic and anaerobic conditions.

RESULTS

Seven of 2050 (0.34%) time-expired PLTs were found repeat reactive by PCR on the initial nucleic acid extract but none of these was confirmed positive on testing frozen second aliquots. BacT/ALERT testing also failed to confirm any time-expired PLTs positive on repeat testing, although 0.24% were reactive on the first test. Three of the 400 "initial-reactive" PLT packs were found by both PCR and BacT/ALERT to be contaminated (Escherichia coli, Listeria monocytogenes, and Streptococcus vestibularis identified) and 14 additional packs were confirmed positive by BacT/ALERT only. In 13 of these cases the contaminating organisms were identified as anaerobic skin or oral commensals and the remaining pack was contaminated with Streptococcus pneumoniae.

CONCLUSION

These results demonstrate that the 16S PCR assay is less sensitive than BacT/ALERT and inappropriate for early testing of concentrates. However, rapid PCR assays such as this may be suitable for a strategy of late or prerelease testing.

Extended storage of autologous apheresis platelets in plasma

BACKGROUND AND OBJECTIVES

The purpose of our studies was to determine the effects of extended platelet storage on poststorage platelet viability.

MATERIALS AND METHODS

Normal subjects were recruited to donate platelets using two different apheresis systems: either the COBE Spectra (n = 58) or the Haemonetics MCS+ (n = 84). Platelet recovery and survival data from the two systems were compared with each other and with in vitro measurements of the stored platelets.

RESULTS

There were no significant differences in either platelet recoveries or survivals between the two machines between 1 and 8 days of storage. Combining the data from both machines, platelet recoveries decreased by 2.6% and survivals by 0.3 days/storage day. In vitro assays did not predict either platelet recoveries or survivals during storage for 5-8 days. After 9 days of storage, pHs were unacceptable (≤ 6.1), suggesting that 8 days will be the longest possible storage time.

CONCLUSIONS

These data suggest that, if stored platelet bacterial contamination issues are resolved, significant extension of platelet storage times is possible.

10 Years Experience with Bacterial Screening of Platelet Concentrates in the Netherlands

SUMMARY: BACKGROUND: Contamination of platelets with bacteria is the major microbiological risk of blood transfusion. Screening for bacterial contamination can reduce the frequency of bacterial transmission considerably. In the present paper, the results of 10-year screening in the Netherlands are described. METHODS: All platelet concentrates were cultured with the BacT/Alert culturing system with large volume (7.5 ml) cultures in either an aerobic or an anaerobic bottle. Products were released on a 'negative-to-date' basis. RESULTS: After introduction of the diversion of the first milliliters of collected blood, the number of positive screening cultures decreased significantly from 0.85% to 0.37%. The frequency of transfusion-transmitted bacterial infections by platelet concentrates is currently less than 1 per 2 years in the Netherlands. CONCLUSION: Over a period of 10 years the bacterial screening system for platelet concentrates proved to result in a safe system with respect to microbiological infection as a result of platelet transfusions.

Implementation of Bacterial Detection Methods into Blood Donor Screening - Overview of Different Technologies

SUMMARY: BACKGROUND: Through the implementation of modern technology, such as nucleic acid testing, over the last two decades, blood safety has improved considerably in that the risk of viral infection is less than 1 in a million blood transfusions. By contrast, the residual risk of transfusion-associated bacterial infection is stable at approximately 1 in 2,000 to 1 in 3,000 in platelets. To improve blood safety with regard to bacterial infections, many countries have implemented bacterial screening methods as part of their blood donor screening programmes. METHODS: BACTERIAL DETECTION METHODS ARE CLUSTERED INTO THREE GROUPS: i) culture methods in combination with the 'negative-to-date' concept, ii) rapid detection systems with a late sample collection, and iii) bedside screening tests. RESULTS: The culture methods are convincing because of their very high analytical sensitivity. Nevertheless, false-negative culture results and subsequent fatalities were reported in several countries. Rapid bacterial systems are characterised as having short testing time but reduced sensitivity. Sample errors are prevented by late sample collection. Finally, bedside tests reduce the risk for sample errors to a minimum, but testing outside of blood donation services may have risks for general testing failures. CONCLUSION: Bacterial screening of blood products, especially platelets, can be performed using a broad range of technologies. Each system exhibits advantages and disadvantages and offers only a temporary solution until a general pathogen inactivation technology is available for all blood components.

Extension of platelet shelf life from 4 to 5 days by implementation of a new screening strategy in Germany

BACKGROUND

The Paul-Ehrlich-Institute analysed all fatalities due to bacterial infections between 1997 and 2007. Thereafter, the platelet shelf life was reduced to a maximum of 4 days after blood donation because the majority of all cases of severe transfusion-transmitted bacterial infections occurred with day 5 platelets. The current study compares the analytical sensitivity and the diagnostic specificity of four rapid bacterial detection procedures.

METHODS

Nine transfusion-relevant bacterial strains were spiked in pooled platelets or apheresis platelets at a low concentration (10 CFU/bag). Samples were collected after day 3, day 4 and day 5 and investigated by four rapid bacterial detection methods (modified BacT/ALERT, Bactiflow, FACS method and 16s DNA PCR methods).

RESULTS

Seven out of nine bacterial strains were adequately detected by BacT/ALERT, Bactiflow and PCR in apheresis platelets and pooled platelets after sample collection at day 3, day 4 and day 5. For three bacterial strains, analytical sensitivity was reduced for the FACS method. Two bacterial strains did not grow under the storage conditions in either pooled or apheresis platelets.

CONCLUSIONS

A late sample collection on day 3, day 4 or day 5 after blood donation in combination with a rapid bacterial detection method offers a new opportunity to improve blood safety and reduce errors due to sampling., BacT/ALERT, Bactiflow or 16s ID-NAT are feasible for late bacterial screening in platelets may provide data which support the extension of platelet shelf life in Germany to 5 days.

Molecular relatedness of Propionibacterium species isolated from blood products and on the skin of blood donors

BACKGROUND

In this study it was investigated whether Propionibacterium acnes present in platelet concentrates (PCs) and related red blood cells (RBCs), originate from the skin of the donor.

STUDY DESIGN AND METHODS

P. acnes that were cultured throughout 2007 and 2008 from PCs and their accompanying RBCs and in 2010 from the phlebotomy site of a selection of the respective donors (n = 22) were typed by amplified fragment length polymorphism. A part of the strains was also determined to species level by sequencing of the 16S rRNA and recA genes.

RESULTS

Three different phylogenetic groups of P. acnes were found. The distribution of the P. acnes in three groups was confirmed by sequencing of the recA gene. All strains that were found in PCs and their accompanying RBCs were identical, which indicates that the strain is already present in the whole blood donation. P. acnes could be found on the skin of almost all screened donors. In eight of 22 cases (36.4%), one of the strains from the donor skin was identical to the strains found in PCs and their accompanying RBCs. In two other cases the strains belonged to the same phylogenetic group.

CONCLUSION

This study supports the theory that the source of P. acnes contamination is in many cases the skin of the donor. However, further study is necessary to rule out other sources of contamination. Because it is difficult to prevent bacterial contamination by P. acnes completely, it is necessary to further investigate the clinical significance of blood products contaminated with P. acnes.

Distribution, origin and contamination risk of coagulase-negative staphylococci from platelet concentrates

Transfusion-associated bacterial sepsis is the most common microbiological risk of transfusion and is caused mostly by platelet concentrates (PCs). The most frequently identified bacterial contaminants of PCs are coagulase-negative staphylococci (CNS). In order to learn more about the distribution, source and risk of the CNS that are involved in bacterial contamination of PCs, CNS strains isolated during platelet screening were collected and characterized to the species level with three different methods: 16S rRNA and sodA gene sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and amplified fragment length polymorphism (AFLP) analysis. AFLP analysis was also used for the typing of the CNS strains. A total of 83 CNS strains were analysed by sequencing and 8 different CNS species were identified, with Staphylococcus epidermidis being the predominant species. MALDI-TOF MS and AFLP analysis confirmed these results to a large extent. However, MALDI_TOF MS could not identify all strains to the species level and AFLP analysis revealed an additional, likely novel, CNS species. The species identified are mainly recognized as being part of the normal skin flora. Typing of the CNS strains by AFLP analysis showed that there was not a unique strain which is significantly more often present during bacterial contamination of PCs.