["The previously reported IMPAACT study was a cluster randomized controlled trial of a patient and physician educational intervention designed to reduce antibiotic prescribing for acute respiratory tract infections (ARIs) in emergency departments (EDs) in the United States. On average, the intervention resulted in a modest improvement in antibiotic prescribing behavior at the end of Year 1 and further improvement after Year 2. Yet the intervention's impact was large at some sites but minimal or even negative at others. A study was undertaken to identify organizational factors that influenced the effectiveness (Organizational Effect Modifiers [OEMs]) of the intervention.", 'Focus groups of nurses and ED staff and semistructured interviews of local project leaders, nurse managers, and quality improvement (QI) officers were performed at seven EDs across the United States. Effectiveness of the local project leader, institutional emphasis on patient satisfaction ratings, and institutional history with and approach to QI were initially identified as key potential OEMs. Two investigators independently read the transcripts for each site and, using prespecified rating scales, rated the presence of each OEM.', 'The perceived effectiveness of the local project leader was most strongly linked to the effectiveness of the intervention. Perceived institutional emphasis on patient satisfaction and institutional history of and approach to QI (top down or bottom up) did not appear to be closely linked with intervention effectiveness.'] Are physician champions key to improving antibiotic prescribing quality?