Fluorescence in situ hybridization using peptide nucleic acid probes (PNA-FISH) differentiates Staphylococcus aureus from other Gram-positive-cocci in clusters (GPCC). 101/202 patients with GPCC+ blood cultures were randomly assigned to clinician-notification of PNA FISH results. Notification was associated with reduced mortality (8% vs.17%, p = 0.05), further antibiotic use (median -2.5 days, p = 0.01), and trended toward reduced hospital stay and charges.