Bacterial sepsis due to bacterial contamination of blood components is an infrequent but potentially serious complication of transfusion. Recently, several studies have reported an increase in the number of bacterially contaminated units in blood bank inventories, particularly in platelet concentrates (1-3). Unlike red cells, platelets are stored at room temperature up to 5 days after collection, an optimal condition for bacterial growth.
Patients at The University of Texas M. D. Anderson Cancer Center are transfused with over 5,000 units of random-donor platelets (RDP) and 500 units of single-donor platelets (SDP) each month. At our center, platelet concentrates are the most frequently transfused blood components during and immediately after chemotherapy, bone marrow transplantation, or peripheral blood stem cell transplantation. Owing to the nature of their disease processes and the therapy instituted, these patients are immunosuppressed and particularly susceptible to infection until the immunological and myelosuppressive effects are overcome. Thus, if bacterial contamination of platelets were to become a significant problem, the impact on our transfusion-dependent patient population here at M. D. Anderson Cancer Center would be enormous.
Despite the increased concern about and clear awareness of the problem, there has been no consensus as to its real extent or practical solutions for dealing with it. Recently, the American Association of Blood Banks (AABB) issued a bulletin to its members to provide information and guidance on issues related to the potential for bacterial contamination of blood and blood components intended for transfusion (4). The AABB recommends that each institution establish its own measures to prevent or minimize the potential for contamination of blood components, and platelet concentrates in particular, until further information becomes available.
In this issue of Current Issues in Transfusion Medicine, we outline the strategies used at M. D. Anderson to prevent bacterial contamination of platelet concentrates. We also assess the extent of the problem in and its effects on our patient population.
Incidence of Bacterial Contamination of Platelets
The reported rates of bacterial contamination vary widely
(from 0% to 10%) depending on the surveillance system used
(1-3,5,6). However, the true incidence of such contamination
is unknown. Septic episodes associated with platelet
transfusions may not be promptly recognized and are
underreported for a number of reasons. Many recipients of
platelet transfusions in our institution also receive large
doses of antibiotics, thus making the diagnosis and
recognition of a potential septic event even more difficult.
The signs and symptoms associated with septic reactions
related to platelet transfusions are similar to those seen in
febrile nonhemolytic transfusion reactions, which are much
more frequent in patients receiving platelets. Other factors
contributing to the underdiagnosis of septic transfusion
reactions include frequent premedication of patients with
antipyretics and antibiotic therapy for underlying sepsis,
which can mask the signs and symptoms associated with the
transfusion of bacterially contaminated platelets.
A report by Morrow et al. suggests that septic reactions may occur as often as 1 per every 4,200 transfusions (3). In that study, all platelet units involved in febrile transfusion reactions were evaluated by Gram staining and culture over a 42-month period. Transfusion-associated sepsis was observed in 7 patients, and 1 of those 7 patients died of sepsis. Also, the incidence of sepsis with platelets stored for 5 days was 5 times higher than with platelets stored 4 days or less.
However, few data exist regarding the true incidence of the bacterial contamination of stored platelets. In a study by Yomtovian et al., Gram staining and microbial culturing of platelet concentrates were done prior to transfusion (7). In a 12-month period, 3,141 RDP pools and 2,476 SDP units were tested. While all SDP units were sterile, 6 of the RDP pools (0.19%) were found to be bacterially contaminated. The contamination rate for units stored less than 4 days was 1.8 per 10,000 units versus 11.9 per 10,000 units for those stored for 5 days. Thus, it would seem that the risk of platelet concentrates becoming contaminated with bacteria is related to the duration of storage. Consequently, Yomtovian et al. recommended shorter platelet storage times or the screening of all 4- and 5-day-old platelets with pretransfusion Gram staining to minimize the risk of a septic transfusion.
We too have studied the problem of bacterial contamination by retrospectively reviewing all bacterial cultures performed on cellular blood components at our institution during the 43- month period from December 1989 to June 1993 (8). We found that, of a total 95,005 RDP units produced, 523 were submitted for culture. Of these, 214 were used for quality control, and 309 were implicated in transfusion reactions. Of the 309 RDP units implicated in transfusion reactions, 15 units (including 4 pools of 4 RDP units) were positive in culture for coagulase-negative Staphylococcus species, 1 unit was positive for Gram-negative rods, and 1 unit was positive for Pseudomonas paucimobilis.
As for SDP units, our review found that, of a total 13,641 units produced, 97 were submitted for culture. Of these, 54 were used for quality control (none showed any evidence of bacterial contamination), and 43 were implicated in transfusion reactions. Two of the SDP units implicated in transfusion reactions showed evidence of contamination (1 unit positive for Gram-variable rods and 1 unit positive for Enterococcus species). It should be noted that none of the patients who received these RDP and SDP units at M. D. Anderson showed evidence of sepsis or other untoward effects and that in all cases the patient was receiving antibiotic therapy.
Strategies for Preventing Transfusion-Associated
Sepsis
Potential sources of contamination include introduction of
bacteria through the phlebotomy site, asymptomatic donor
bacteremia, defects in plastic storage bags, prolonged
storage, and exposure during the pooling procedure. In
recognizing the potential deleterious effects of bacterial
contamination on a susceptible population, we have
implemented and now practice at M. D. Anderson a series of
preventive measures (Table 1).
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Pivotal in this scheme is our insistence on transfusing, when possible, SDP units stored for no more than 1 day and RDP units stored for no more than 3 days. This strategy is logistically possible because we collect and prepare platelets in our own blood bank without relying on outside sources. We do not believe that bacteriological screening, such as Gram staining, of all platelets prior to infusion is practical or necessary in a clinical setting such as ours where 150-200 RDP units and 20 SDP units are transfused daily. We also insist on pooling RDP only after the order for transfusion has been received and the courier or orderly is ready to pick up the pool of platelets. Moreover, our nursing personnel are trained in (a) the importance of infusing the platelets as soon as they are delivered to the inpatient ward or outpatient clinic and (b) the relevance of identifying and reporting any transfusion reaction possibly due to bacterial contamination.
Conclusion
We recommend that every transfusion service review its own
procedures for preparing and manipulating platelets in order
to detect possible weaknesses or flaws that may lead to the
introduction or proliferation of bacteria. We suggest that
efforts be made to reduce the likelihood of contamination.
Also, we recommend that new practical methods be explored for
establishing whether platelets are contaminated before they
are ever infused into patients.
The task of minimizing the risk of bacterial contamination of platelets is not simple because the problem is multifaceted and has many variables. Yet, heightened awareness of the serious damage that may be done to the immunosuppressed patient by infusing contaminated platelets can become the driving force in finding the solution.
References
2. Cunningham M, Cash JD. Bacterial contamination of platelet concentrates stored at 20 degrees C. J Clin Pathol 26:401-404, 1973.
3. Morrow JF, Braine HG, Kickler TS, et al. Septic reactions to platelet transfusion: A persistent problem. JAMA 266:555-558, 1991.
4. Svoboda R, Lipton KS. Bacterial contamination of blood components. American Association of Blood Banks Association Bulletin #96-6, 1996.
5. Katz AJ, Tilton RC. Sterility of platelet concentrates stored at 25 degrees C. Transfusion 10:329-330, 1970.
6. Wrenn HE, Speicher CE. Platelet concentrates: Sterility of 400 single units stored at room temperature. Transfusion 14:171-172, 1974.
7. Yomtovian R, Lazarus HM, Goodnough LT, et al. A prospective microbiologic surveillance program to detect and prevent the transfusion of bacterially contaminated platelets. Transfusion 33:902-909, 1993.
8. Alvarez FE, Rogge KJ, Tarrand J, Lichtiger B. Bacterial contamination of cellular blood components: A retrospective review at a large cancer center. Ann Clin Lab Sci 25:283-290, 1995.