Diagnosing periprosthetic infection: false-positive intraoperative Gram stains.

Background: Intraoperative Gram stains have a reported low sensitivity but high specificity when used to help diagnose periprosthetic infections. In early 2008, we recognized an unexpectedly high frequency of apparent false-positive Gram stains from revision arthroplasties.

Questions/purposes: The purpose of this report is to describe the cause of these false-positive test results.