A Superficial Swab Culture is Useful for Microbiologic Diagnosis in Acute Prosthetic Joint Infections

The literature documents poor concordance between superficial swab and intraoperative tissue cultures in chronic prosthetic joint infections but is less clear in acute postsurgical prosthetic joint infections. We evaluated the relationship between superficial swab and deep intraoperative cultures in 56 patients with acute postsurgical prosthetic joint infections from June 2003 to June 2007; patients receiving antibiotics were excluded. There were 30 hip and 26 knee prostheses. A superficial sample of the wound drainage was taken at admission and three deep samples were obtained during open d,bridement. Concordance was defined when at least one of the microorganisms isolated in the superficial samples also was found in the deep samples. The analysis also was performed according to the type of microorganism: Staphylococcus aureus, gram-negative bacilli, or other gram-positive microorganisms. Concordance between superficial and deep samples was 80.3% (45 of 56). The sensitivity, specificity, and positive and negative predictive values of superficial cultures to predict the microorganism isolated in deep cultures varied depending on the type of microorganism: 93.7%, 100%, 100%, and 97.5% for S. aureus; 90%, 91.6%, 85.7%, and 94.3% for gram-negative bacilli; and 50%, 75%, 60%, and 66.7% for other gram-positive microorganisms. We therefore believe the superficial swab culture is useful in identifying the etiologic microorganism of acute prosthetic joint infections, especially when S. aureus or gram-negative bacilli were identified. Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.