Bacterial Contamination of Platelets

The evaluation of microbial contamination in platelet concentrates prepared by two different methods

The microbial contamination of platelet concentrates (PCs) prepared by two different methods both with a high risk of bacterial contamination during preparation and storage were evaluated. For apheresis platelets, the concentrates were obtained using the Haemonetics MCS 3P device. For the random method, platelets were obtained by two phase centrifugation, in the Heraeus Cryofuge 8500 I device using the Kansuk 3-way bags which permit storage for five days. 1620 plateletpheresis units prepared by apheresis, and 9838 units prepared by the random method, were included in the study. Of the 11,458 PCs studied. 32 (0.27%) were false positives and 24 (0.2%) were real positives. All of the positive results occurred in platelets prepared by the random method. C. xerosis and S. epidermidis, S. hominis, Alpha-hemolytic streptococci, all flora of the skin, were isolated in the contaminated concentrates. The risk of microbial contamination of PCs, prepared both by apheresis and from whole blood, continues at a low rate although the products were collected into specific bags following rules including appropriate disinfection of the skin, correct centrifugation collection time and optimal storage conditions including temperature and agitation. These results again emphasize the importance of: obeying phlebotomy rules and hand disinfection of the person who collects the blood as well as the need for careful skin decontamination of the donor, during donation.

Bacterial decontamination of blood stem cell apheresis products

High-dose chemotherapy using autologous bone marrow or mobilized blood as the source of stem cells for haematologic rescue, is being widely used for a variety of haematological malignancies and solid tumours. To collect sufficient numbers of haematopoietic stem cells for successful engraftment, standard apheresis procedures are performed. Newer techniques and refinements of the procedure allow using only 1 to 2 apheresis products (AP) for autografting. Bacterial contamination of the AP, although very rare, sometimes occurs and may lead to generalized infection in the recipient. The apheresis must be repeated, sometimes even including time-consuming and costly mobilization. At our institution, the patients' blood stem cells are usually mobilized with chemotherapy followed by daily s.c. haematopoietic growth factor injections or with growth factor alone. An apheresis machine is used for collection through a central venous line and the AP is routinely checked for bacterial contamination. Results are only available after the product has been processed and cryopreserved. In the last 5 years, we observed bacterial contamination in four of our AP. Therefore, we investigated the possibility of in vitro antibiotic decontamination. Using standard antibiograms, we determined the sensitivities of the contaminating bacteria. By incubating the products with the specific antibiotics at bactericidal concentrations, we were able to sterilize the probes from the contaminating bacteria. In the concurrently performed controls without the active substance, bacteria were still detectable. We conclude that in selected cases, in vitro decontamination using pretested antibiotics, may be a feasible, cost-effective, and easy alternative to performing additional apheresis procedures.

Fatal Clostridium perfringens sepsis from a pooled platelet transfusion

A male patient with acute myeloid leukaemia received a pooled platelet preparation prepared by Optipress system on the last day of its shelf life. The patient collapsed after two-thirds of the contents had been transfused. Clostridium perfringens was isolated from the platelet bag within 18 h of the acute event. Metronidazole, gentamicin and Clostridium antiserum were then administered in addition to the broad spectrum antibiotics started previously. However, the patient died 4 days after the platelets were transfused. The cause of death was given as cardiovascular shock, entirely compatible with an overwhelming bacteraemic and septic episode. A coroner's verdict of accidental death due to transfusion of a contaminated unit of platelets was recorded. On subsequent investigation Cl. perfringens type A serotype PS68,PS80 (identical to that found in the platelet bag) was cultured from the venepuncture site of the arm of one of the donors who contributed towards the platelet pool. The donor had two young children and frequently changed nappies. Faecal contamination of the venepuncture site was the suspected source for the transmission of Cl. perfringens, an organism commonly found in the soil and intestinal tract of humans. This case dramatically highlights the consequences of transfusing a bacterially contaminated unit. It is vital that such incidents are investigated and reported so that the extent of transfusion-associated bacterial transmission can be monitored and preventative measures taken if possible.

Possible implication of sterile connecting device in contamination of pooled platelet concentrates

Considering the possibility that a pooled random donor platelet concentrate could become contaminated by welding with a sterile connecting device, we undertook a study to determine the influence of pooling on the contamination rate. As a control group, apheresis platelets were examined. Bacteriological testing was done with a sensitive CO2 detecting culture system, the BacT/ Alert. Out of 1105 pooled platelet concentrates prepared by the buffy coat method, 15 (1.4%) were confirmed as contaminated, all with Staphylococcus epidermidis and two with a second bacterial species, i.e. Staphylococcus capitis and Propionibacterium acnes, respectively. Median detection time by the BacT/Alert was 23 h. Twelve pools of five units were contaminated, which is significantly more than the three contaminated pools of four units. On the other hand, the reuse of the welding wafers proved not be a risk factor for contamination. One welded tubing segment of a contaminated platelet concentrate failed the air leakage test, an incident which was 73 times more frequent than with the sterile platelet concentrates. We found five pooled platelet concentrates containing Staphylococci from which no bacteria could be grown from the individual buffy coats that had been pooled. We suggest the contamination here to have occurred after separation of the buffy coat from the whole blood, possibly during the welding process. Finally, none out of 378 apheresis platelet concentrates was contaminated. All our observations highlight the potential risk for contamination when making pooled platelet concentrates with a sterile connecting device. For this type of transfusion product, we advocate bacteriological screening of all units before release. The incubation time for the sterility test should, however, be limited to 36 h, if logistical problems with the availability of platelets are to be avoided.

A retrospective analysis of microbial contaminants in outdated random-donor platelets from multiple sites

BACKGROUND

Platelet components contaminated with bacteria are an important source of transfusion-associated bacterial sepsis. Estimates of contamination rates vary widely (0-10%) and are highly controversial. The present study, designed with stringent testing regimens, retrospectively determined the prevalence of microbial contaminants in platelets from four collection regions.

STUDY DESIGN AND METHODS

During a 9-month period, outdated platelet units were assayed by spreading aliquots from the unit, and from thioglycollate broth medium inoculated with part of the unit, onto 5-percent sheep blood agar media. Cultures were examined after 72-hour incubation at 37 degrees C, and, if bacterial growth was present, the assay processes were repeated with fresh inocula. Units were considered contaminated only if repeatedly positive.

RESULTS

Four (0.08%) of 4995 units sampled were contaminated, two with Corynebacterium sp. and one each with Propionibacterium acnes and Aspergillus terreus. Contaminants were present at low, subclinical levels and were detected only after amplification in thioglycollate. The contaminated units were cultured 1, 2, 3, and 7 days after expiration.

CONCLUSION

Contamination rates were low and did not vary by region. The identification of A. terreus suggests the role that transfusion may play in transmitting fungal infections should be reassessed. The persistent detection of contaminated platelet units supports the need for a test to detect clinically relevant levels of microbial contaminants in blood components.

Sources and sequelae of bacterial contamination of hematopoietic stem cell components: implications for the safety of hematotherapy and graft engineering

BACKGROUND

It is important to compare the incidence of bacterial contamination of components collected from the peripheral blood or bone marrow (BM), as well as of components processed with or without cell selection or depletion, and to evaluate the sequelae of such contamination.

STUDY DESIGN AND METHODS

Bacterial contamination rates were compared in 1380 untreated autologous peripheral blood progenitor cells (PBPCs), 291 untreated autologous BM samples, 916 monoclonal antibody (MoAb)-treated autologous and allogeneic BM samples, and in 45 autologous PBPC components from which the CD34+ cells were selected. Bacterial cultures were performed at sequential time points during the processing of MoAb-treated BM.

RESULTS

Bacterial contamination was documented in 44 of 2632 components from 1593 patients (1.67% of components, 2.76% of patients) before cryopreservation. Although only 0.65% of untreated PBPCs were contaminated before cryopreservation, each patient was more likely to have given a contaminated PBPC component than a contaminated BM component (2.41% vs. 0%, p < 0.01). Bacterial contamination of MoAb-treated BM was greater during or after manipulation than it was before (2.33% vs. 0.77%, p < 0.05). At thawing, contamination was documented in 42 (1.97%) of 2136 components cultured. Ten (13.7%) of 73 patients who received hematopoietic progenitor cells that were contaminated before cryopreservation or at thawing developed fever or positive blood cultures within 48 hours of transfusion. Fever was associated with bacteremia in two cases, but no irreversible clinical sequelae were noted.

CONCLUSION

These studies suggest that, despite careful attention to sterile procedures, low-level contamination of hematopoietic stem cell components can be introduced before or during manipulation as well as at thawing, and that standards for monitoring of the procedures for collection, processing, cryopreservation, thawing, and transfusion of hematopoietic progenitor cells are necessary.

[Quality assurance of bacterial incidents associated with blood transfusion]

Transfusion associated bacterial sepsis, TABS, may be caused by-donor bacteremia,-bacteria from the donors skin,-bacteria brought by one of the persons handling the donation or the blood product, from collection and components preparation to the actual transfusion,-or bacteria introduced by a defect in one of the disposables used. Quality Assurance relies on the Good Transfusion Practices of the French Blood Agency all along the transfusion chain from the donor to the recipient. Active involvement of personnel, standardisation and controls as well as improvement of technics particularly as regarding donor selection, skin disinfection technics and collection are required. The ultimate control is hemovigilance with proper identification and investigation of all cases of TABS even with mild symptoms. Centralisation of data in the Haemovigilance scheme is a further step toward a better understanding and improvement of blood products bacterial security.

Transfusion reactions: the changing priorities

Over the last dozen years the relative frequencies of specific transfusion reactions have markedly altered, in general for the better. Although AIDS remains the Public's primary concern, the risk of AIDS from a transfusion is extremely low at this point. Hepatitis remains the most common infectious complication of blood transfusion, but only 1 in 6,000 units now carry a risk, whereas in the early 1980's the risk is believed to have been close to 10% per patient. Transmission of HTLV-I/II has also been markedly reduced by tests of donor sera. In contrast, cytomegalovirus has become of increased importance in view of the large number of patients immunosuppressed for transplantation and cancer therapy; bacterial growth in blood components appears to be increasingly common; and Chagas disease is likely to become a serious transfusion problem in this country. More widespread use of filters which remove three logs or more of white blood cells from components should play a major role in reducing transfusion reactions further.