Bacterial Contamination of Platelets
For the past several years, bacterial contamination of platelets has been the greatest transfusion-transmitted infectious risk in the United States; this risk has been significantly higher than the risk of transfusion-transmitted viral infection. Bacterial contamination of platelet components occurs because the storage temperature for platelets (22° C) may facilitate bacterial growth. Approximately 1 in 1,000-3,000 platelet units may be contaminated with bacteria. Transfusion-transmitted sepsis has been recognized and culture-confirmed in at least 1 of 100,000 recipients, and has led to immediate fatal outcome in 1 in 500,000 recipients. The actual risk of transfusion-associated sepsis is likely higher, as infections due to contaminated blood products are under-reported.
It is critical that clinicians be aware of the problem of bacterial contamination of blood products, particularly platelets, and consider the possibility of bacterial contamination when investigating febrile transfusion reactions. Clinicians should collaborate with hospital transfusion services and blood collection center personnel, and, when necessary, notify health departments, to manage suspected infections in blood donors and patients.
Protocols should be in place to help clinicians recognize and manage transfusion reactions, including those potentially caused by bacterial contamination. Post-transfusion notification of appropriate personnel is needed if cultures identify slow-growing bacteria after product release or transfusion.
If bacterial contamination of a component is suspected, the transfusion should be stopped immediately, the unit saved for further testing, and blood cultures should be obtained from the patient. Bacterial isolates from cultures of the recipient and unit should be saved for further investigation.
For any gram-negative or clinically significant gram-positive organisms, it is recommended that the donor be carefully examined for evidence of occult infection, particularly if the organism identified could be potentially harmful to the donor or if the organism has been detected previously in the same donor. Any organism of public health significance identified in donors or recipients will require notification of the appropriate state and local public health department. In addition, the organism should be saved for confirmation of identity and further investigation.
To address the three most common situations clinicians may face:
- Clinician is contacted after transfusion of a unit with positive test results;
- a recipient develops post-transfusion bacteremia after receiving platelets; and
- a blood donor is identified as potentially infected.
AABB, formerly known as the American Association of Blood Banks, is now only known by its acronym.
Clinician is contacted by the blood collection or transfusion service with information involving a blood or blood component with bacterial contamination.
- The minimal evaluation of a patient suspected of having received a bacterially contaminated platelet transfusion should include
- culture of any residual component, if available, to confirm the initial result, and
- blood cultures of the patient, even in the absence of apparent sepsis, to be certain that clinically silent infections are not missed.
- Any isolates (i.e., microorganisms obtained from the residual component and/or patient culture) should be retained until the case investigation is completed. This permits detailed studies to determine if the microorganisms are linked.
- Results of the patients clinical and laboratory workup should be communicated to the transfusion service medical director who in turn should report these findings to the collection facility.
A blood or blood component recipient has signs or symptoms consistent with post-transfusion bacteremia. Because no test is 100% sensitive, false-negative results of platelet screening for bacterial contamination will occur.
- Transfusing physicians should continue to evaluate all transfused patients with onset of signs or symptoms consistent with bacteremia or sepsis for a transfusion reaction.
- The minimal evaluation of a patient with suspected sepsis following platelet transfusion should include
- culture of any residual component, if available, and
- blood cultures of the patient.
- Any isolates should be retained until the case investigation is completed.
- Results of the patient workup should be communicated to the transfusion service medical director and the medical director of the collection facility; these data will help determine the significance of the initially negative test result.
A blood donor presents to clinician with concerns of a “medically significant abnormality” discovered during the blood donation process.
- Donors with potentially medically significant microorganisms may be advised to see their physician for further evaluation. Evaluation of the donor by the physician should begin with a thorough clinical history and a physical examination. Follow-up investigations might include blood cultures, other body site cultures, and additional tests as appropriate.
- Communication between blood center physician and clinician should facilitate management of the donor. Identification of a culture indicating endogenous bacteremia will likely result in deferral of the donor from future blood donation. To resume donation, the donor may be required to be cleared by the clinician and the blood center medical director; this could be based on the donor successfully completing treatment.
Bacterial contamination of platelet components is the second most common cause of transfusion-related deaths in the United States. To address this risk, the AABB adopted a standard that requires blood collection and transfusion service members to detect and limit bacterial contamination in all platelet components. However, currently there is no single test used to detect bacteria in platelet units, and regardless of the method, bacterial screening of platelets is unlikely to detect all pathogens.
Bacterial contamination of a blood component usually is not considered in the differential diagnosis of transfusion-related illness because signs and symptoms (including fever, rigors, and change in blood pressure) resemble those expected from either transfusion reaction or from sepsis due to any cause. Gram-positive organisms (e.g. Staphylococcus epidermidis) found on skin are the most frequent contaminants of platelet units. Although less commonly recognized as contaminants, gram-negative bacteria (e.g., Serratia, Enterobacter, Salmonella spp.) cause more severe and often fatal infections.
The AABB Standard
To address the risk of bacterial contamination, effective March 1, 2004, the AABB adopted standard 18.104.22.168 (Standards for blood Banks and Transfusion Services, 22nd edition) that requires all accredited institutional members to “implement measures to detect and limit bacterial contamination in all platelet components.” The College of American Pathologists has also added a query on such testing to the transfusion medicine checklist of their Laboratory Accreditation Program.
At this time no single test is used to detect bacteria in platelet units. In practice, the type of platelet donation (apheresis or whole blood-derived platelets) has dictated the bacterial detection approach. Most blood collection centers culture apheresis platelets (derived from single donors), and release the unit after the culture has incubated between 24-36 hours. In most cases, bacterial screening of whole-blood derived platelets (pooled from 4–6 donations) is conducted by hospital transfusion services. Many hospitals have implemented point of use tests, such as glucose and pH indicators, to screen whole-blood derived platelets, that may result in more frequent false-negative results.
AABB Guidance for Implementation
In an effort to improve bacterial screening and reporting, AABB has provided guidance on standardized definitions for test results, investigation and product management of implicated platelet units with positive tests, management of other components (co-components) associated with the same donation, and further characterization of detected organisms.
This guidance for the blood collection or transfusion service recommends that the following actions be taken:
- When Bacterial Contamination is Found in the Unit After Transfusion
Because culture-based tests take variable amounts of time to generate positive results, bacterial contamination may be identified after the unit has been released and transfused.
- Prompt notification to the transfusing physician with all available information must be made according to local operating procedures either by the transfusion service or the facility performing the testing.
- All test results should be reported to the transfusion service medical director and the transfusing physician as soon as possible.
- A Gram’s stain should be performed immediately on any retained portion of the unit.
- The microorganism should be identified and susceptibility testing performed promptly.
- Post transfusion patient follow-up care will depend on the clinical status of the transfused patient and the judgment of the transfusing physician. Direct communication between the medical director of the testing facility and the transfusion service medical director, and between either of these individuals and the transfusing clinician, is important for optimal management of patient care decisions.
- When Possible Donor Infection Associated with Organisms Found on Bacterial Testing is Suspected
Before the performance of confirmatory assays, initial test results will include both true and false positives. The initial positive test result may be either true contamination introduced from the donor or during handling, or a false-positive result. False- positive results may be due to the poor specificity of surrogate tests (e.g. pH, glucose) or, for culture-based tests, due to laboratory contamination of the culture system during handling. True positive results may occur with a wide variety of organisms; while many may be of little or no clinical significance to the donor, others may be more significant. A true positive result is most often the result of contamination of the platelet unit by skin flora (due to incomplete skin decontamination or as a result of a skin plug). However, a true positive result can also be the result of organisms that may be of clinical significance to the donor, including those that cause bacteremia. Gram-negative organisms (e.g., Eschericia. coli) most often are due to occult bacteremia. All gram-negative organisms should be considered potentially significant for the donor’s health. Gram-positive organisms (e.g., Staphylococcus epidermidis) are likely to be either skin commensals or environmental contaminants. However, some gram positive organisms (e.g., Staphylococcus aureus, Streptococcus pneumoniae) may be from endogenous bacteremia in the donor. For example, an organism such as S. aureus may originate from a bacteremia in a patient whose osteomyleitis was incompletely treated. Moreover, some organisms may have low pathogenicity, but may indicate a significant underlying disease (e.g., Streptococcus bovis bacteremia associated with colon cancer).
- Blood collection facilities must notify donors of any medically significant abnormality discovered either during the interview or detected as a result of laboratory testing, in compliance with standard 5.2.2 of the 22nd edition of Standards for Blood Banks and Transfusion Services of the AABB. Deferral criteria are established by the Food and Drug Administration (FDA) or applicable State Department of Health (or applicable regulatory agency), or by guidelines from the facility medical director; they are based on the severity and transmissibility of the disease and on the availability of a confirmatory test.
- Certain organisms are of important public health significance, regardless of effects on donor health. These organisms require additional consideration and reporting according to local and national guidelines. (See: Examples of Organisms of Public Health Significance.)
Reporting requirements may vary by state, follow reporting criteria set forth by local authorities.
Bacterial Category A Agents of Bioterrorism
- Bacillus anthracis
- Yersinia pestis
- Francisella tularensis
- Clostridium botulinum
- Immediate Report to Public Health Authorities
- (Save Isolates for Confirmatory Identification and further Action)
Other selected bacteria associated with nationally notifiable diseases
- Listeria monocytogenes
- Salmonella(all spp.)
- Shigella (all spp.)
- Group A Streptococcus
- Streptococcus pneumoniae
- Neisseria meningitidis
- Neisseria gonorrhoeae
- Report to Health Authorities
- (Save Isolates for Confirmatory Identification and further Action)