A retrospective analysis of microbial contaminants in outdated random-donor platelets from multiple sites

Platelet components contaminated with bacteria are an important source of transfusion-associated bacterial sepsis. Estimates of contamination rates vary widely (0-10%) and are highly controversial. The present study, designed with stringent testing regimens, retrospectively determined the prevalence of microbial contaminants in platelets from four collection regions.

During a 9-month period, outdated platelet units were assayed by spreading aliquots from the unit, and from thioglycollate broth medium inoculated with part of the unit, onto 5-percent sheep blood agar media. Cultures were examined after 72-hour incubation at 37 degrees C, and, if bacterial growth was present, the assay processes were repeated with fresh inocula. Units were considered contaminated only if repeatedly positive.

Four (0.08%) of 4995 units sampled were contaminated, two with Corynebacterium sp. and one each with Propionibacterium acnes and Aspergillus terreus. Contaminants were present at low, subclinical levels and were detected only after amplification in thioglycollate. The contaminated units were cultured 1, 2, 3, and 7 days after expiration.

Contamination rates were low and did not vary by region. The identification of A. terreus suggests the role that transfusion may play in transmitting fungal infections should be reassessed. The persistent detection of contaminated platelet units supports the need for a test to detect clinically relevant levels of microbial contaminants in blood components.