title: Early Versus Late Culture Growth of Propionibacterium acnes in Revision Shoulder Arthroplasty.
abstract: BACKGROUND
  Propionibacterium acnes is recognized as a pathogenic organism associated with periprosthetic joint infection following shoulder arthroplasty. The goal of our study was to determine the relationship between the time to P. acnes growth in culture and the likelihood of a culture result being a true positive versus a false positive based on the proportion of positive cultures and other perioperative findings in cases of revision shoulder arthroplasty.
  
  
  METHODS
  We retrospectively reviewed forty-six cases with P. acnes-positive cultures among patients who underwent revision shoulder arthroplasty between May 2010 and October 2014. Tissue and fluid was cultured anaerobically for a mean (and standard deviation) of 13.1 ± 3 days. Cases were categorized into one of two groups for analysis: probable true positive or probable contaminant (false-positive) on the basis of culture results and perioperative findings.
  
  
  RESULTS
  The time to P. acnes culture growth was significantly shorter (p = 0.002) in the probable true-positive culture group compared with the probable contaminant group (median of five days [interquartile range, four to seven days]) compared with nine days [interquartile range, six to twelve days]). Among the thirty-seven cases in the probable true-positive group, no culture result turned positive after eleven days, whereas in the probable contaminant group, cultures turned positive after this time point in 44% (four of nine) of the cases. There were also significantly fewer days to P. acnes culture growth among cases with a higher number of positive cultures (p = 0.001) and a higher proportion of positive cultures (p < 0.001), regardless of group classification.
  
  
  CONCLUSIONS
  P. acnes is the most commonly identified organism following revision shoulder arthroplasty. The proportion of positive cultures and the timing of culture growth may help to distinguish a true-positive from a false-positive culture result.
  
  
  METHODS
  Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue - A40, Cleveland, OH 44195. E-mail address for E.T. Ricchetti: ricchee@ccf.org.
authors.forename: Salvatore J
authors.initials: SJ
authors.lastname: Frangiamore
authors.affiliation: Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue - A40, Cleveland, OH 44195. E-mail address for E.T. Ricchetti: ricchee@ccf.org.
authors.forename: Anas
authors.initials: A
authors.lastname: Saleh
authors.affiliation: Cleveland Clinic Lerner College of Medicine, 9500 Euclid Avenue - NA21, Cleveland, OH 44195.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Grosso
authors.affiliation: Division of Orthopaedic Surgery, Hamilton General Hospital, 237 Barton Street East, Hamilton, ON L8L 2X2, Canada.
authors.forename: Bashar
authors.initials: B
authors.lastname: Alolabi
authors.affiliation: Pathology and Laboratory Medicine Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue - L21, Cleveland, OH 44195.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Bauer
authors.affiliation: Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue - A40, Cleveland, OH 44195. E-mail address for E.T. Ricchetti: ricchee@ccf.org.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Iannotti
authors.affiliation: Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue - A40, Cleveland, OH 44195. E-mail address for E.T. Ricchetti: ricchee@ccf.org.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Ricchetti
mesh_terms: D001178:Arthroplasty; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011425:Propionibacterium acnes / Q000254:growth & development* / Q000302:isolation & purification; D012086:Reoperation; D012189:Retrospective Studies; D012785:Shoulder Joint / Q000382:microbiology / Q000601:surgery*; D013997:Time Factors