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Bacterial Contamination

Blood components are sterile. However, if bacteria are introduced into donor units during collection, processing, or pooling, they may cause sepsis or life-threatening endotoxic shock. Recent data has demonstrated that 1 in 70,000 to 1 in 118,000 aphereis platelet units are associated with a septic transfusion reaction.

Etiology: Contamination of the donor unit with skin flora at the time of collection is the most common cause of bacterial contamination. A small core of skin containing bacteria may enter the phlebotomy needle during skin puncture. Needles, anticoagulant-preservative solution or the plastic blood collection bags and tubing may become contaminated with airborne or waterborne bacteria. Other bacterial isolates are less likely to colonize skin and have been associated with recent illness, underlying disease or exposure to exotic pets. Low level or episodic bacteremia may occur in donors with gastroenteritis, gastrointestinal cancer, upper respiratory tract infections, periodontal disease, dental procedures or endocarditis.

Septic reactions are more common after platelet than red blood cell transfusions. Platelets are stored for up to five days at room temperature and provide better growth media for bacteria than do refrigerated red blood cells. The risk of bacterial contamination is less for single donor apheresis platelets than for pooled random donor platelet concentrates.

Symptoms: Most septic transfusion reactions become symptomatic during the transfusion or within 4 hours afterward. Transfusion associated sepsis should be considered in a patient who develops fever of 39 C (102.2 F) or higher which may be accompanied by rigors, tachycardia or change in heart rate of 40 beats per minute or greater, or a rise or fall in blood pressure of 30 mm Hg, dyspnea, and nausea or vomiting. Shock, hemolysis, renal failure, and disseminated intravascular coagulation may also be present. Patients under general anesthesia may develop hypotension, oliguria and excessive bleeding.

Consequences: Transfusion of a bacterially contaminated blood component is potentially fatal. It must be recognized and treated immediately. The reported rate of fatal transfusion reactions due to bacterial sepsis has been less than 1 in a million.

Lab data: The transfusion should be stopped immediately and the bag, tubing and other fluids being administered should be returned to the transfusion service for immediate investigation. The bag should be inspected for discoloration, clots or hemolysis. A Gram stain and blood culture should be performed on an aliquot of blood from the bag and from the recipient. Blood should be inoculated into a set of aerobic and anaerobic blood culture bottles and incubated for 5 to 7 days. A positive Gram stain indicates a heavily contaminated unit. The Gram stain may be negative in one third of cases even though contamination is present.

Most Commonly Isolated Bacterial Contaminants

Platelets

Red Cells

Staphylococcus aureus

Yersinia enterocolitica

Klebsiella

Serratia species

Seratia

Pseudomonas species

Staphylococcus epidermidis

Streptococcus viridans

Salmonella

Pseudomonas

Enterobacter

E. coli

Bacillus

Proteus mirabilis

Isolation of the same organism from the blood bag and the patient establishes the diagnosis of bacterial contamination with a high degree of certainty. Bacterial strain genotyping can be performed to further confirm that the bacteria in the blood bag and patient are identical. If the patient is receiving antibiotics at the time of transfusion, blood cultures from the patient may be negative for the organism in question.

The possibility of inadvertent contamination of the component after transfusion should be considered if there is significant delay or mishandling of the unit prior to culture. A sterile component can also become cross-contaminated by a bacteremic patient’s blood and have a positive culture. In this case, the Gram stain of the residual component is unlikely to be positive.

If no blood component is remaining, 20 mL of culture media or sterile saline should be aseptically injected into the bag, mixed and inoculated into the culture bottles. Segments attached to the blood bag are not a reliable source to detect bacterial contamination.

Treatment: The patient’s physician should be notified immediately. If the patient is not already being treated with IV antibiotics, they should be started as quickly as possible.

Occasionally, the blood center may notify the hospital transfusion service that the blood culture of a unit has turned positive after platelets have already been transfused. . In this case, the recipient should be evaluated for any signs or symptoms of a septic transfusion reaction that may not have been reported to the transfusion service. If the patient appears clinically well, further clinical observation may be more appropriate than prophylactic antibiotics.

Prevention: Many precautions have been implemented to prevent bacterial contamination including taking donor temperatures, questioning donors about recent infections, optimizing skin disinfection before phlebotomy and diverting an initial aliquot of blood collected during phlebotomy. Each apheresis platelet unit is cultured from the first day after collection until it outdates. If bacterial growth is detected in a unit, a blood center immediately notifies the hospital transfusion service. The hospital transfusion service then takes the following actions:

  • If the unit has not been transfused, it is immediately quarantined and returned to the blood center. The blood center will also quarantine any co-components from the same donation.
  • If the unit has already been transfused to an inpatient, the nursing unit is immediately notified.
  • If the unit has already been transfused to an outpatient, the ordering physician is immediately contacted.

Currently there are two FDA approved culture-based methods for bacterial detection, the BacT-ALERT system and the Pall enhanced Bacterial Detection System (eBDS). Unfortunately, the sensitivity of bacterial culture is only 25% based on true positive rates of both aerobic and obligate anaerobic organisms. Gram stains exhibit even less sensitive.

All policies involving collection, handling, and storage of blood components must be carefully followed. All blood components should be inspected prior to transfusion for any abnormal color, opacity, hemolysis or clots. Suspect units should not be issued for transfusion.The infusion set should be primed and the blood bag spiked using aseptic technique. Transfusions should be begun as soon as the units are available and the transfusion completed within 4 hours to prevent possible bacterial proliferation. If the transfusion cannot be started within 30 minutes the unit should be promptly returned to the Blood Bank for proper storage. If a unit is contaminated, all other blood components from that donation should be immediately recalled.

The blood supplier should be notified by the hospital transfusion service immediately when bacterial contamination is suspected so that other components collected from the implicated donor can be quarantined.

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