Recent Advances in Preventing Adverse Reactions to Transfusion

The spectrum of adverse reactions to blood product transfusion ranges from a benign clinical course to serious morbidity and mortality.  There have been many advances in technologies and transfusion strategies to decrease the risk of adverse reactions. Our aim is to address a few of the advancements in increasing the safety of the blood supply, specifically pathogen reduction technologies, bacterial contamination risk reduction, and transfusion associated acute lung injury risk mitigation strategies.

Treatment of Platelet Products with Riboflavin and UV Light: Effectiveness Against High Titer Bacterial Contamination

Contamination of platelet units by bacteria has long been acknowledged as a significant transfusion risk due to their post-donation storage conditions. Products are routinely stored at 22 °C on an agitating shaker, a condition that can promote bacterial growth. Although the total number of bacteria believed to be introduced into a platelet product is extremely low, these bacteria can multiply to a very high titer prior to transfusion, potentially resulting in serious adverse events. The aim of this study was to evaluate a riboflavin based pathogen reduction process against a panel of bacteria that have been identified as common contaminants of platelet products. This panel included the following organisms: S. epidermidis, S. aureus, S. mitis, S. pyogenes, S. marcescens, Y. enterocolitica, B. neotomae, B. cereus, E. coli, P. aeruginosa and K. pneumoniae. Each platelet unit was inoculated with a high bacterial load and samples were removed both before and after treatment. A colony forming assay, using an end point dilution scheme, was used to determine the pre-treatment and post-treatment bacterial titers. Log reduction was calculated by subtracting the post-treatment titer from the pre-treatment titer. The following log reductions were observed: S. epidermidis 4.7 log (99.998%), S. aureus 4.8 log (99.998%), S. mitis 3.7 log (99.98%), S. pyogenes 2.6 log (99.7%), S. marcescens 4.0 log (99.99%), Y. enterocolitica 3.3 log (99.95%), B. neotomae 5.4 log (99.9996%), B. cereus 2.6 log (99.7%), E. coli ≥5.4 log (99.9996%), P. aeruginosa 4.7 log (99.998%) and K. pneumoniae 2.8 log (99.8%). The results from this study suggest the process could help to lower the risk of severe adverse transfusion events associated with bacterial contamination.

Split Blood Products

The last 20 years have seen many advances in transfusion therapy and safety. Blood products are biological products engendering complex interactions with the immune system. Prestorage leukoreduction results in a reduced risk of febrile reactions, CMV transmission, and immune modulation, proving to be safer for patients than non-leuko reduced products.

Simple patient identification issues and clerical error continue to be the primary causes of ABO-incompatible transfusions. Rigorous donor screening as well as serologic and nucleic acid testing for transfusion transmitted infection have brought the blood supply to a very safe level, although transmission of these agents continues to be a problem in underdeveloped countries. Emerging infectious diseases, beyond current laboratory detection capabilities, combined with global travel, pose unknown imminent risks everywhere. We also briefly discuss the current risks of transfusion-transmitted infections.

We review currently available hemostatic blood products, their compositions, and their clinical indications; we mention product modifications currently in development; and we touch upon the hemostatic properties and drawbacks of whole blood, which is currently gaining popularity as an alternative to split blood products. We conclude with an in-depth overview of the risks associated with transfusion, including incompatibility, hemolytic transfusion reactions, transfusion-associated circulatory overload (TACO), and transfusion-related acute lung injury (TRALI).

Routine bacterial screening of platelet concentrates by flow cytometry and its impact on product safety and supply

BACKGROUND AND OBJECTIVES

Bacterial contamination represents the major infectious hazard associated with transfusion of platelet concentrates (PCs). As bacterial screening of PCs is not mandatory in Germany, the BactiFlow flow cytometry test has been introduced as a rapid detection method to increase product safety.

MATERIALS AND METHODS

During a period of 25 months, a total of 34 631 PCs (26 411 pooled and 8220 apheresis-derived PCs) were tested at the end of day 3 of their shelf life using the BactiFlow system. PCs initially reactive in BactiFlow testing and expired PCs not reactive in BactiFlow on day 3 were also investigated by the BacT/ALERT system and by microbiological cultivation in order to identify the contaminating bacterial species and to confirm reactive BactiFlow results.

RESULTS

Two hundred and twenty-eight PCs (0.7%) had an initially reactive result, 24 of them remained reactive in a second test run. Out of these reproducible reactive BactiFlow results, 12 could not be verified by parallel BacT/ALERT culturing, resulting in a confirmed false-positive rate of 0.03%. The bacterial species were identified as S. aureus, S. epidermidis, S. dysgalactiae ssp. equisimilis and B. cereus. In 10 out of 9017 expired PCs (0.11%), a confirmed-positive result was obtained in the BacT/ALERT system which had a negative result in the BactiFlow system.

CONCLUSION

Testing of PCs by BactiFlow was successfully implemented in our blood donation service and proved sufficient as a rapid and reliable screening method. False reactive results are in an acceptable range since the transfusion of 12 bacterially contaminated PCs was prevented.

One size will never fit all: the future of research in pediatric transfusion medicine

There is concern at the National Heart, Lung, and Blood Institute (NHLBI) and among transfusion medicine specialists regarding the small number of investigators and studies in the field of pediatric transfusion medicine (PTM). Accordingly, the objective of this article is to provide a snapshot of the clinical and translational PTM research considered to be of high priority by pediatricians, neonatologists, and transfusion medicine specialists. Included is a targeted review of three research areas of importance: (i) transfusion strategies, (ii) short- and long-term clinical consequences, and (iii) transfusion-transmitted infectious diseases. The recommendations by PTM and transfusion medicine specialists represent opportunities and innovative strategies to execute translational research, observational studies, and clinical trials of high relevance to PTM. With the explosion of new biomedical knowledge and increasingly sophisticated methodologies over the past decade, this is an exciting time to consider transfusion medicine as a paradigm for addressing questions related to fields such as cell biology, immunology, neurodevelopment, outcomes research, and many others. Increased awareness of PTM as an important, fertile field and the promotion of accompanying opportunities will help establish PTM as a viable career option and advance basic and clinical investigation to improve the health and wellbeing of children.

Safety of platelet transfusion: past, present and future

Platelet components became routinely available to many institutions in the late 1960s and since then utilization has steadily increased. Platelets are produced by three principal methods and their manufacturing process is regulated by multiple agencies. As the field of platelet transfusion has evolved, a broad array of strategies to improve platelet safety has developed. This review will explore the evolution of modern platelet component therapy, highlight the various risks associated with platelet transfusion and describe risk reduction strategies that have been implemented to improve platelet transfusion safety. In closing, the reader will be briefly introduced to select investigational platelet and platelet-mimetic products that have the potential to enhance platelet transfusion safety in the near future.

An inhibition of p38 mitogen activated protein kinase delays the platelet storage lesion

BACKGROUND AND OBJECTIVES

Platelets during storage undergo diverse alterations collectively known as the platelet storage lesion, including metabolic, morphological, functional and structural changes. Some changes correlate with activation of p38 mitogen activated protein kinase (p38 MAPK). Another MAPK, extracellular signal-related kinase (ERK), is involved in PLT activation. The aim of this study was to compare the properties of platelets stored in plasma in the presence or absence of p38 and ERK MAPK inhibitors.

MATERIALS AND METHODS

A single Trima apheresis platelet unit (n = 12) was aliquoted into five CLX storage bags. Two aliquots were continuously agitated with or without MAPK inhibitors. Two aliquots were subjected to 48 hours of interruption of agitation with or without MAPK inhibitors. One aliquot contained the same amount of solvent vehicle used to deliver the inhibitor. Platelets were stored at 20-24°C for 7 days and sampled on Days 1, 4, and 7 for 18 in vitro parameters.

RESULTS

Inhibition of p38 MAPK by VX-702 leads to better maintenance of all platelet in vitro storage parameters including platelet mitochondrial function. Accelerated by interruption of agitation, the platelet storage lesion of units stored with VX-702 was diminished to that of platelets stored with continuous agitation. Inhibition of ERK MAPK did not ameliorate decrements in any in vitro platelet properties.

CONCLUSION

Signaling through p38 MAPK, but not ERK, is associated with platelet deterioration during storage.

[Control of the bacterial risk of transfusion in France in 2013]

Bacterial contamination of blood products (BP) remains the most important infectious risks of blood transfusion in 2013. Platelet concentrates (PC) are the blood products the most at risk, whether CPA or MCPS. In France, the residual risk has been steadily declining since 1994. For the platelets, the frequency of transfusion reaction due to bacterial contamination (TRBC) is now about at one per 50,000 CP distributed. The number of deaths has remained stable since 1994 with one death per year (300,000 distributed CP). The progressive decrease in the number of cases of TRBCs is the result of steady improvement of practices and prevention methods at all stages from collection to the transfusion of BP. But if all these improvements have significantly reduced the incidence of TRBCs, mortality is not changed with the CP and the reduction of this risk is a priority for the French Blood Establishment (EFS). Detection methods of CP contaminated or pathogen inactivation are two approaches available and can provide a significant reduction (for the former) or deletion (for seconds) of the risk of transfused contaminated CP. Currently, the choice is in favor of the detection of bacteria. New detection "rapid tests" methods were added to the panel of candidates and are being evaluated. Inactivation of pathogens remains the safest prospect of eliminating this adverse effect of transfusion. Implementation of one method for bacterial detection is probably a transitional measure.

Routine use of a rapid test to detect bacteria at the time of issue for nonleukoreduced, whole blood-derived platelets

BACKGROUND

The Pan Genera detection (PGD) test is used to screen platelet (PLT) products for bacterial contamination. We report the experience of using the PGD test on whole blood-derived PLTs (WBPs) at two large centralized transfusion services (CTS).

STUDY DESIGN AND METHODS

Records of PGD test results were retrospectively reviewed. The PGD test was performed on individual WBP units or pools of WBPs ranging in size from 2 to 6 units at the time of issue. Bacterial culture was performed on PLT products with positive PGD tests, and at one CTS, the available cocomponents.

RESULTS

A total of 70,561 WBP pools were screened with the PGD test. There were seven true-positive PGD tests and 242 false-positive tests (positive predictive value of PGD test, 2.81%). The overall contamination rate was 99 per 10(6) WBP pools (1:10,080; 95% confidence interval [CI], 40-204), and the false-positive rate was 3430 per 10(6) WBP pools (1:292; 95% CI, 3011-3890). All seven bacterial isolates were Gram positive. The median age of the individual WBP units in the seven contaminated pools was 5 days (range, 3-5 days) compared to 4 days (range, 1-5 days) in the false-positive pools (p=0.0012). The same bacteria isolated from a positive PLT pool also grew in one red blood cell cocomponent.

CONCLUSION

After testing more than 70,000 WBP pools at two large CTSs, the rate of contaminated WBP pools detected by the PGD test was 99 per 10(6) pools (1:10,080).

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.

Therapeutic efficacy of platelet components treated with amotosalen and ultraviolet A pathogen inactivation method: results of a meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVES

There are conflicting data regarding the therapeutic efficacy of platelets inactivated using amotosalen and ultraviolet A light. We have performed a meta-analysis to summarize the results of different randomized controlled trials (RCT).

MATERIALS AND METHODS

Five RCTs reported through March 2011 met the criteria for meta-analysis. Weighted mean difference (WMD) in corrected count increment (CCI) at 1 h, CCI-24 h, and transfusion interval (days) and summary odds ratio (OR) of bleeding in inactivated platelet (I-P) group vs. noninactivated platelet (C-P) group were calculated across studies.

RESULTS

Randomized controlled trials were statistically homogeneous when we analysed CCI-24 h, and the transfusion of C-P was associated with a higher CCI-24 h when compared with the transfusion of I-P (WMD, 3×10(3); 95% CI, 2·32×10(3)-3·69×10(3); P<0·00001). RCTs were statistically heterogeneous when we analysed CCI-1 h, transfusion interval and OR of bleeding. Regarding the OR of bleeding in the I-P and C-P groups, it varied by as much as a multiple of four among the trials, from 0·66 to 2·66. When we combined double-blinded and high methodologic quality score RCTs, the use of I-P was not statistically associated with an increase in the OR of bleeding when compared with the use of C-P (OR, 0·97; 95% CI, 0·75-1·27; P=0·84).

CONCLUSION

Although the transfusion of I-P was associated with lower CCI-24 h when compared with the transfusion of C-P, this was not associated with differences in the OR of bleeding between I-P and C-P.

Alternative blood products and clinical needs in transfusion medicine

The primary focus of national blood programs is the provision of a safe and adequate blood supply. This goal is dependent on regular voluntary donations and a regulatory infrastructure that establishes and enforces standards for blood safety. Progress in ex vivo expansion of blood cells from cell sources including peripheral blood, cord blood, induced pluripotent stem cells, and human embryonic stem cell lines will likely make alternative transfusion products available for clinical use in the near future. Initially, alloimmunized patients and individuals with rare blood types are most likely to benefit from alternative products. However, in developed nations voluntary blood donations are projected to be inadequate in the future as blood usage by individuals 60 years and older increases. In developing nations economic and political challenges may impede progress in attaining self-sufficiency. Under these circumstances, ex vivo generated red cells may be needed to supplement the general blood supply.

Effect of Safety Measures on Bacterial Contamination Rates of Blood Components in Germany

SUMMARY: Requirements for bacterial testing of blood components on a defined quantity as part of routine quality control were introduced in Germany by the National Advisory Committee Blood of the German Federal Ministry of Health in 1997. The philosophy was to establish standardized methods for bacterial testing. Numerous measures to reduce the risk of bacterial contamination were implemented into the blood donation and manufacturing processes between 1999 and 2002. German Blood establishments performed culture-based bacterial testing on random samples of platelet concentrates (PCs), red blood cells (RBCs) and fresh frozen plasma (FFP) and reported data out of the production periods 1998, 2001 and 2005/2006. While the bacterial contamination rate of apheresis PCs remained nearly unchanged, it decreased by 70% for pooled PCs to a rate of 0.158% in the last observation period. Leukocyte-depleted RBCs with diversion of the initial blood volume showed a contamination rate of 0.029% which is significantly lower than that of RBCs without leukocyte depletion and diversion (0.157%). The contamination rate of plasma decreased by 80%. Preventive measures resulted in a significant reduction of bacterial contamination of blood components. Long-term monitoring with standardized methods for bacteria testing supports evaluation of the cumulative effect of contamination reducing measures.

Transfusion-Transmitted Bacterial Infections - Haemovigilance Data of German Blood Establishments (1997-2010)

SUMMARY: METHODS: In order to evaluate the benefit of risk minimisation measures, reporting rates of transfusion-transmitted bacterial infections (TTBI) were calculated on the basis of annual reports and distributed blood components. Following the implementation of risk minimisation measures in 2003 and 2008, a comparison of pre- and post-implementation periods was performed. RESULTS: During a period of 14 years, 90 cases of TTBI were confirmed, 34 were caused by red blood cell (RBC) concentrates, 5 by fresh frozen plasma, and 51 by platelet concentrates (PCs). The overall reporting frequency was 1 TTBI in 1.91 million RBC units; 1 TTBI in 0.094 million PC units, and 1 TTBI-associated fatality in 0.57 million PC units. From 2001-2004 the reporting rate was 13.7 per million PC units; 2005-2008, after the implementation of pre-donation sampling; it was 10.8 per million PC units (p > 0.5). After limitation of the shelf life (2008), the reporting rate decreased to 4.49 per million PC units (p = 0.12), and one case of related fatality was reported. Agents with low pathogenicity were reported in 14 of 41 immunosuppressed patients (34%) but only in 1 of 13 patients with non-haematological/oncological diseases. CONCLUSION: TTBI and associated fatalities could be gradually reduced by the risk minimisation measures, but further strategies such as implementation of sensitive screening tests or pathogen-reducing approaches should be discussed.

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.

Laboratory Evaluation of the Effectiveness of Pathogen Reduction Procedures for Bacteria

SUMMARY: Bacterial contamination remains a leading factor for transfusion-associated serious morbidity and mortality. Pathogen reduction procedures offer a pro-active approach to prevent bacterial contamination of cellular blood components and especially of platelet concentrates. In the past, the laboratory evaluation of the effectiveness of the pathogen reduction procedures to minimise the bacterial load of blood components has been primarily based on log reduction assays similar to the assessment of antiviral activities. Bacteria strains with the ability to multiply in the blood components are seeded in highest possible cell numbers, the pathogen reduction procedure is applied, and the post-treatment number of bacteria is measured. The effectiveness of the procedure is characterised by calculating the log reduction of the post- to pre-treatment bacteria titres. More recently, protocols have been developed for experiments starting with a low bacteria load and monitoring the sterility of the blood component during the entire storage period of the blood component. Results for 3 different pathogen reduction technologies in these experimental models are compared and critical determinants for the results are addressed. The heterogeneity of results observed for different strains suggests that the introduction of international transfusion-relevant bacterial reference strains may facilitate the validity of findings in pathogen reduction experiments.

Bacterial contamination in platelets: incremental improvements drive down but do not eliminate risk

BACKGROUND

Bacterial contamination of platelet components (PCs) remains an important cause of transfusion-associated infectious risk. In 2004, Canadian Blood Services (CBS) implemented bacterial testing of PCs using the BacT/ALERT 3D system (bioMérieux). This system has been validated and implemented and continuous monitoring of culture rates allows gathering of data regarding true and false positives as well as false negatives.

STUDY DESIGN AND METHODS

National data gathered between March 2004 and October 2010 from 12 CBS sites were analyzed to compare bacterial contamination rates across three platelet (PLT) preparation methods: apheresis, buffy coat, and PLT-rich plasma. Data were compared before and after implementation of protocol changes that may affect bacterial detection or contamination rates.

RESULTS

Initial positive rates among the three production methods were significantly different, with apheresis PCs being the highest. The rates of confirmed positives among production methods did not differ significantly (p = 0.668). Increasing sample testing volumes from 4 to 6 mL to 8 to 10 mL significantly increased the rate of initial positives, while confirmed positives increased from 0.64 to 1.63 per 10,000, approaching significance (p = 0.055). Changing the skin disinfection method from a two-step to a one-step protocol did not significantly alter the rate of confirmed positives. During the period of data analysis, eight false-negative cases were reported, with five implicated in adverse transfusion reactions.

CONCLUSION

Bacterial testing of PCs and implementation of improved protocols are incrementally effective in reducing the risk of transfusion of bacterially contaminated PLT concentrates; however, the continued occurrence of false-negative results means the risk has not been eliminated.

Screening of platelets for bacterial contamination at the Welsh Blood Service

BACKGROUND AND OBJECTIVE

This report details the results of the implementation of a bacterial screening system at the Welsh Blood Service and provides an estimate of the levels of bacterial contamination at the time of sampling.

MATERIALS AND METHODS

Apheresis (Caridian BCT) and buffy coat-derived pooled platelet components were sampled on day 1 for bacterial contamination and the sample was monitored throughout the lifespan of the platelet component. Unused platelet components were re-tested to determine the effectiveness of the screening. Results from the BacT/ALERT are uploaded to the in-house Blood Establishment Computer System (BECS) every 12 min. Positive alerts are automatically sent to staff, facilitating a timely intervention.

RESULTS

Between February 2003 and March 2010 the screening system tested 54 828 platelets and detected 257 (1 in 213) initial positives of which 35 (1 in 1567, 0·06%) were confirmed [95% confidence interval (CI), 0·04-0·08%]. Additionally, screening of 6438 unused platelet components detected another 6 (1 in 1073, 0·09%) confirmed positives not detected during initial testing (95% CI, 0·02-0·16%). Analysis of the data suggests that on day 1 the number of bacteria in such platelet component packs was between 5 and 62 cfus total. Day 1 culture has a sensitivity of 40%.

CONCLUSIONS

The bacterial screening system has removed a significant number, but not all bacterially contaminated platelet components from the supply. The sample volume is an important factor in sensitivity due to the low number of bacteria in a platelet component pack on day 1. An effective notification and recall system is a critical part of the bacterial screening system.

Storage age of transfused platelets and outcomes after cardiac surgery

BACKGROUND

The relationship between duration of platelet (PLT) storage, currently limited to 5days, and surgical outcomes has not been established. We tested the hypothesis that PLT storage age was associated with adverse outcomes.

STUDY DESIGN AND METHODS

A retrospective cohort of aortocoronary bypass (CABG) surgery patients from January 1996 to January 2005 receiving one or more PLT transfusions was selected for study. The composite primary ("short-term") outcome was 30-day mortality or prolonged hospital stay. Secondary outcomes included complications and survival to annual follow-up. Multivariable logistic regression models and Cox proportional hazards regression analysis evaluated the association between PLT storage age and outcomes, expressed as an odds ratio (OR) or hazard ratio with 95% confidence intervals (CIs), respectively.

RESULTS

PLT transfusion was administered to 3272 of 10,275 CABG patients and 2578 received units of known storage age, which ranged between 2 and 5days (median, 4days; 25th percentile, 3days; 75th percentile, 5 days). The mortality rate for the 1637 patients receiving a single plateletpheresis transfusion was 3.8%, while 21.6% experienced a prolonged hospital stay or death. After adjusting for the number of PLT and red blood cell (RBC) units transfused, RBC storage age, and preoperative mortality risk, there was no association between PLT storage age and short-term outcome (OR, 1.01; 95% CI, 0.90-1.14), survival (hazard ratio [HR], 1.04; 95% CI, 0.96-1.13), or postoperative infections.

CONCLUSIONS

PLT storage age was not associated with adverse short-term outcomes, decreased long-term survival, or infections after cardiac surgery.

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.