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Bacterial Screening
Bacterial contamination of blood components may result in septic transfusion reactions ( Chapter 67 ), which can be fatal. Platelet products, particularly those on day 4 or 5 of storage, are most commonly associated with these reactions because they are stored at room temperature in nutrient media (plasma) enabling bacteria growth. Technologies have been developed to mitigate risk of bacterial contamination of platelet products, including methods to avoid or decrease bacterial contamination, inactivate bacteria, and detect contamination. Each method offers advantages and limitations. In addition, new strategies are being developed.
Risk of septic reaction was first addressed by AABB with Standard 5.1.5.1, requiring blood collection agencies implement methods to limit and detect bacteria in platelet products. This resulted in improved collection methods, with skin cleansing and diversion pouches, and use of bacterial detection methods, including culture. These steps decrease septic reaction rate from reported range of 10–400 to 7–25 in 1,000,000 and fatal septic reaction rate from reported range of 2–63 to 2–12 in 1,000,000 apheresis platelet products transfused. Thus, implementation of bacterial screening has apparently decreased the overall risk by approximately 2/3, but the FDA has issued several iterations of a draft guidance intended to further reduce this risk. This chapter will address methods used to limit and detect bacterial contamination in platelet products ( Table 19.1 ).
Table 19.1
Methods to Reduce Bacterial Contamination
| Bacterial contamination avoidance | Donor eligibility |
| Collection platform | |
| Skin preparation | |
| Bacterial contamination reduction | Diversion pouch or, on automated collections, return of initial 50-100 ml of collection volume to donor |
| Bacterial contamination inhibition | Cold, cryopreserved, or lyophilized storage a |
| Storage solutions | |
| Bacterial contamination inactivation | Pathogen inactivation |
| Bacterial contamination detection | Culture |
| Nucleic acid testing a | |
| Point of release immunoassays |
While cold storage of platelets is not currently licensed, several centers are preparing and transfusing cold stored platelets under IND.
Methods to Minimize Bacterial Contamination
Donor Screening
Donor eligibility questions are used to exclude donors with fever, with symptomatic infections, or receiving antibiotics for infection. Donor screening does not eliminate donors with asymptomatic infections, which may include gram-negative bacteria, resulting in severe septic transfusion reactions.
Skin Preparation
Skin is the source of contamination for ∼80% of bacterially contaminated units. Skin decontamination with iodine decreases bacterial contamination. Chlorhexidine has been documented to be more effective in reducing bacterial contamination in studies measuring residual colonies, although large-scale studies showing fewer septic reactions are lacking. Consequently, many centers offer both, with many using iodine–povidone as default and chlorhexidine after donor reports of skin reaction.
Diversion Pouch
Bacteria within hair follicles and scar tissue (typically observed in repeat donors) may not be completely eliminated by skin preparation. Sample diversion pouch collects skin plug and first ∼50 mL of blood, which further reduces product contamination; Staphylococcus species bacterial contamination decreased from 0.14% to 0.03% of units. Blood samples collected from diversion pouch are used for infectious disease testing.
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