BACKGROUND: Bacterial contamination is currently the most important infectious risk associated with transfusion of platelet (PLT) products. Prestorage culture has reduced but not eliminated this problem. STUDY DESIGN AND METHODS: Eighteen hospitals studied the Pan Genera Detection (PGD) test, a rapid, lateral-flow immunoassay for the detection of Gram-positive and Gram-negative bacteria. The PGD test was performed on day of issue on apheresis PLTs released by collection centers as culture negative. Confirmatory bacterial culture was performed when PGD tests were repeatedly reactive, with three sites performing culture on all doses studied. RESULTS: PGD tests on nine of 27,620 (1:3069, 95% confidence interval [CI] 1:6711 to 1:1617; or 326 per million, 95% CI 149-618 per million) apheresis PLT doses were repeatedly reactive and verified as bacterially contaminated by confirmatory culture. Bacterial species isolated included coagulase-negative staphylococci (n = 6), Bacillus sp. (n = 2), and Enterococcus faecalis (n = 1). The ages of these contaminated doses were Day 3 (n = 4), Day 4 (n = 2), and Day 5 (n = 3). Two contaminated doses with nonreactive PGD tests were detected among 10,424 doses at hospitals where concurrent culture was performed, and one other was identified via a transfusion reaction investigation. There were 142 PGD false positives (0.51%). CONCLUSIONS: The PGD test detected bacterial contamination in 1:3069 (9 of 27,620) doses released as negative by prestorage culture in PLTs as young as 3 days old. Three contaminated doses, two clinically insignificant, had nonreactive PGD tests, while 0.51% of tests were false positives. Application of this test on day of issue can interdict contaminated units and prevent transfusion reactions.