The Fate of the Unexpected Positive Intraoperative Cultures After Revision Total Knee Arthroplasty.  Robert L. Barrack,  Ajay Aggarwal,  R. Stephen J. Burnett,  John C. Clohisy,  Elie Ghanem,  Peter Sharkey and Javad Parvizi.  Washington University & Barnes-Jewish Hosp., St. Louis, MO;  Thomas Jefferson University & Rothman Inst,  Philadelphia, PA.  Journal of Arthroplasty, 2007; 22(6) pp94-99.

-Of a consecutive series of 692 revision total knees at 3 centers, intra-operative cultures were unexpectedly found to be positive in 41cases (5.9%). Of the 41, 29 (71%) cases had a single positive intra-operative culture and were determined to be a probable false positive based on absence of any other evidence of infection, of which 5 were treated with extended course of intravenous antibiotics after hospital discharge and the remaining 24 received no further treatment. None of these 24 patients manifested any sign of infection at follow-up, averaging 46 months (range, 24-74 months): Staph. epi (46%); enterococcus (11%); Staph. aureus (14%); Strep (9%); Corynebact. (7%); Diptheroids(7%); Prop. Acne(4%). Twelve patients were determined to have probable type 1 peri-prosthetic infection, 11 of which were treated with a course of antibiotics: Staph. epi.(50%); Enterococcus 29%; Staph. aureus 7%; MRSE (7%); Strep(7%).   Two (18%) of these patients became re-infected within one year.  CONCLUSION: A single positive intra-operative culture after revision total knee arthroplasty does not mandate further treatment in the absence of any other signs of infection.  DR. CIERNY’S COMMENTS: THIS ARTICLE EMPHASIZES TWO VERY IMPORTANT POINTS WHEN SENDING WOUND  CULTURES: 1) ALWAYS SEND MORE THAN ONE SPECIMEN WHEN CULTURING A WOUND. —–  FALSE POSITIVE CULTURES DO OCCUR;  2) BIOPSY WHAT YOU CULTURE AND CULTURE WHAT YOU BIOPSY.  A  POSITIVE CULTURE +  TISSUE WITH NO EVIDENCE OF ACUTE INFLAMMATION = A FALSE POSITIVE CULTURE.  IF, HOWEVER, THERE IS A POSITIVE CULTURE WITH POSITIVE HISTOLOGY IN AN UNEXPECTED SCENARIO FOLLOWING IMPLANTATION OF HARDWARE (SEE PROTOCOL),  AT THE VERY LEAST WE WOULD RECOMMEND OPEN IRRIGATION/DEBRIDEMENT OFTHE WOUND, SYSTEMIC ANTIBIOTICS AND ANTIBIOTIC-DEPOT FILLING OF THE ADJACENT DEAD SPACE.