title: Swab cultures are not as effective as tissue cultures for diagnosis of periprosthetic joint infection.
abstract: BACKGROUND
  While it is accepted accurate identification of infecting organisms is crucial in guiding treatment of periprosthetic joint infection (PJI), there remains no consensus regarding the best method for obtaining cultures.
  
  
  OBJECTIVE
  We compared the yield of intraoperative tissue samples versus swab cultures in diagnosing PJI.
  
  
  METHODS
  Tissue and swab cultures (three each) were collected prospectively during a consecutive series of 156 aseptic and septic revision arthroplasties from October 2011 to April 2012. The tissues and swabs were taken from standardized regions of the joint. After excluding 39 reimplantation procedures, we included 117 cases (74 hip, 43 knee; 30 septic, 87 aseptic) for analysis. We used a modified version of the Musculoskeletal Infection Society criteria for defining PJI, requiring three of five rather than four of six criteria. Tissue and swab cultures from septic and aseptic cases were used to calculate their sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for identifying PJI.
  
  
  RESULTS
  Tissue cultures were positive in a higher percentage of septic cases than swab cultures: 28 of 30 (93%) versus 21 of 30 (70%). Tissue cultures were positive in two of 87 aseptic cases (2%), while swab cultures were positive in 10 of 87 (12%). The sensitivity, specificity, PPV, and NPV were 93%, 98%, 93%, and 98%, respectively, for tissue cultures and 70%, 89%, 68%, and 90%, respectively, for swab cultures.
  
  
  CONCLUSIONS
  Tissue cultures demonstrated higher sensitivity, specificity, PPV, and NPV for diagnosing PJI than swab cultures. Swab cultures had more false-negative and false-positive results than tissue cultures. Because swab cultures pose a higher risk of not identifying or incorrectly identifying infecting organisms in PJI, we believe their use in obtaining intraoperative culture specimens should be discouraged.
  
  
  METHODS
  Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Rothman Institute of Orthopedics at Thomas Jefferson Hospital, 925 Chestnut Street, Philadelphia, PA, 19107, USA.
authors.forename: Vinay K
authors.initials: VK
authors.lastname: Aggarwal
authors.forename: Carlos
authors.initials: C
authors.lastname: Higuera
authors.forename: Gregory
authors.initials: G
authors.lastname: Deirmengian
authors.forename: Javad
authors.initials: J
authors.lastname: Parvizi
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Austin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006621:Hip Joint / Q000382:microbiology* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007719:Knee Joint / Q000382:microbiology* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D011446:Prospective Studies; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000382:microbiology / Q000601:surgery; D012086:Reoperation; D013048:Specimen Handling; D046509:Tissue Culture Techniques