Bacterial contamination of blood and its cellular components remains the most common infectious cause of transfusion associated morbidity and mortality. Septic transfusion reactions are the second most common cause of transfusion-associated death in Western countries after blood type incompatibility reaction. Bacterial infections can be a result of environmental contamination during collection and processing, donor or recipient skin colonization or donor bacteremia. As a result, the most predominant bacteria isolated are usually commensals of the skin or gastrointestinal tract flora. 

Measures to reduce the risk of bacterial contamination focus on different steps in the transfusion chain:

Donor eligibility: To reduce asymptomatic donor bacteremia, subjects with recent dental treatments, minor surgery or increased body temperature at presentation should be excluded from donation;
Optimal product processing, handling and storage: Continuous training and supervision of the responsible personnel for donation and product processing are key elements for high quality standards and product safety. Also, consistent storage temperatures (4°C for red blood cells and 22–24°C for platelets) need to be maintained to ensure product integrity;
Skin preparation: Improved donor arm disinfection has been shown to be crucial in reducing the numbers of remaining bacteria on the phlebotomy puncture site (44, 45, 46), even if there is uncertainty about the most effective regimen for reducing the microbial load (the number of microscopic bacterial organisms) on the donor arm;
Removal of the initial whole blood collection (diversion): It has been shown that removal of the first 30–40 ml of whole blood from the collection bag might reduce the contamination risk from skin bacteria. In fact, improved donor arm disinfection in association with blood diversion has been reported to reduce the risk of bacterial contamination by up to 77% (47, 48, 49).
Bacterial detection methods: Different methods have been investigated for detecting bacteria in platelet components including an automated bacterial culture method, direct bacterial staining, bacterial endotoxin and ribosomal assays, nucleic acids testing for bacterial DNA, and measures of O2 consumption or CO2 production (50,51,52,53). However, none of these detection methods seems to identify all bacterial contaminations and additional bacterial screening tests as well as better timing of bacterial testing (i.e. closer to the time of transfusion) might be needed to further improve the likelihood of correctly identifying bacterially contaminated blood products;
Pathogen reduction methods: The goal of pathogen inactivation is to reduce the risk of known and unknown pathogens susceptible to the treatment applied, without compromising therapeutic efficacy of the blood product or introducing secondary risks. It offers a log reduction and not necessarily elimination of   infectivity of susceptible agents and requires monitoring for break-through infections.