A cluster of bacterial contamination of platelets occurred at a university hospital in a one-month period. This unusual clustering allowed us to examine the likely mechanism of contamination and clinical sequelae.

We reviewed medical records of patients receiving random donor platelet transfusions to determine numbers of platelets transfused, reactions reported, and episodes of bacterial contamination. We also reviewed procedures at the collecting blood agencies and the hospital blood bank.

Four patients received bacterially contaminated platelets during June and July 1991. The rates of reported platelet transfusion reactions increased significantly (P<0.001) from September 1989 through July 1991 (study period); in addition, the rate of contamination of platelets during June and July 1991 was 23-fold higher than during the previous 21 months (P< 0.00 1). Surveillance methodology changed dramatically during the study period, contributing to the recognition of the current cluster. Pathogens isolated from the contaminated platelet pools were Bacillus cereus, Staphylococcus epidermidis, or Pseudomonas aeruginosa in titers ranging from 106 to 108 colony forming units/ml. Four constituent individual platelet units identified as the probable cause of the outbreak (including one postepidemic episode) were significantly older (mean age, 4.8 days) than 106 randomly selected individual platelet units (mean age, 3.7 days; P = 0.04). Platelet pools were transfused an average of 2.5 hours after pooling. Review of blood collection and platelet preparation practices did not identify breaks in procedure or technique that could have caused contamination.

Increased awareness of platelet transfusion reactions by clinical staff and routine culturing of all platelets associated with transfusion reactions will identify contaminated platelets. Identification of contaminated platelets is necessary to treat affected patients appropriately and to determine the prevalence of and risk factors for contaminated platelets.