Bacterial Contamination of Platelets: The Effect on Patient Outcome.

Bacterial contamination of blood components is an important cause of transfusion-related morbidity and mortality. Platelets in particular are susceptible to contamination, as they are stored at room temperature for up to five days. It is estimated that 1 in every 2000 units of platelets is contaminated with bacteria.

The current study is a retrospective analysis of bacterially contaminated platelet pools and the effect on the patients transfused. Bacterially contaminated pooled platelets transfused between November 16, 2005, and March 3, 2006, were identified, along with the species of bacteria. Records of the patients transfused with these pools were analyzed to assess for signs / symptoms of transfusion-associated sepsis (fever and hypotension during and after the transfusion), and whether antibiotics had been administered prior to the transfusion.

Of the 5,676 platelet pools transfused between November 16, 2005, and March 3, 2006, 46 (0.8%) were bacterially contaminated. Platelets more than 3 days old are not transfused. The majority of bacteria isolated consisted of normal skin flora. See Table. None of the patients experienced an increase in temperature more than 1°C between the time the transfusion started and four to six hours after it was completed. Three patients had a temperature of more than 38 °C after the transfusion. In two of the patients, the post-transfusion temperature had actually decreased, even though it remained above 38 °C. The other patient had a pre-transfusion temperature of 37.8 °C and a post-transfusion temperature of 38.4 °C; this was not reported at the time as a febrile transfusion reaction.

None of the patients developed hypotension severe enough to warrant interrupting the transfusion. One patient had blood pressure of 98/60 immediately following the transfusion, but the pre-transfusion blood pressure was 111/65. None of the other patients had systolic pressure less than 100 post-transfusion.

Thirty-five patients were receiving antibiotics at the time of transfusion. Of these, two had positive blood cultures (coagulase negative staphylococcus and enterococcus faecium) after the transfusion, although their blood cultures were also positive for these bacteria prior to the transfusion. None of the patients not receiving antibiotics had positive blood cultures.

0.8% of pooled platelets transfused were contaminated, most of them with skin flora. None of these pools had a detrimental effect on the patients. Although most of the patients were receiving antibiotics due to their underlying diseases, none developed either clinical symptoms of sepsis or positive blood cultures due to transfusion of the contaminated platelets.

Platelets in our institution are stored for a maximum of three days. It is possible that transfusion was completed before the bacteria in the unit reached a significant level. Our findings and experience clearly point out that transfusion of platelets of one to three days of age may not have a detrimental clinical impact. Our current policy follows the practice described of releasing pools of platelets before the bacterial cultures are completed and resulted. Additional research is needed to determine how many colony forming units are present in the platelet units at three days and again at five days, and the impact on patient outcome.