title: Clinical impact of positive Propionibacterium acnes cultures in orthopedic surgery.
abstract: The clinical significance of a positive culture to Propionibacterium acnes in orthopedic specimens remains unclear, whether about its role as a contaminant or a pathogen, or its impact as a coinfectant. Therefore, we performed a retrospective study to provide a more accurate description of the clinical impact of P. acnes in an orthopedic population aiming to determine: 1) if there is a clinical difference between P. acnes infection and contamination? 2) If there is a clinical difference between P. acnes monoinfection, and coinfection.
  
  
  
  There is a clinical difference between P. acnes infection and contamination.
  
  
  
  Patients were selected over a five-year period, and those with a minimum of one positive culture for P. acnes, from any intraoperative orthopedic tissue sample, were included in the study. P. acnes infection was defined as the isolation of P. acnes from≥2 specimens, or in only one specimen, in the presence of typical perioperative findings and/or local signs of infection.
  
  
  
  A total of 68 patients had a positive P. acnes culture, 35 of which were considered to be infected. The infections affected mostly males (29/35-83%), occurred mostly in shoulders (22/35-63%), and at a site already containing an orthopedic implant (32/35-91%). Local inflammatory signs were present in half of the cases when an infection was diagnosed. Coinfection with other pathogens was present in 31% of patients (11/35). When comparing patients coinfected with P. acnes, and those who were monoinfected, the latter presented less often with local inflammatory signs. Recurrence rate was 24% (8/35) and the only risk factor for recurrence was the presence of a monoinfection.
  
  
  
  This study confirms the pathogenicity of P. acnes in an orthopedic population, as it is present in multiple samples in the same patient, and because it is present in cultures from cases with clinical recurrence. Our study showed that monoinfections differ from coinfections mainly by their higher risk of recurrence.
  
  
  
  Level IV retrospective case series.
authors.affiliation: Service de microbiologie médicale et infectiologie, hôpital du Sacré-Cœur de Montréal, 5400, boulevard Gouin O, C-2095, Montréal, H4J 1C5 Québec, Canada; Faculté de microbiologie, infectiologie et immunologie, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4 Québec, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Lavergne
authors.affiliation: Faculté de médecine, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4e Québec, Canada; Service de chirurgie orthopédique, hôpital du Sacré-Cœur de Montréal, 5400, boulevard Gouin O, C-2095, H4J 1C5 Montreal, Quebec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Malo
authors.affiliation: Orthopedic Surgery service, Red Deer Regional Hospital, 3942 50a Ave, Red Deer, T4N 4E7 AB, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Gaudelli
authors.affiliation: Faculté de médecine, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4e Québec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Laprade
authors.affiliation: Faculté de médecine, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4e Québec, Canada; Service de chirurgie orthopédique, hôpital du Sacré-Cœur de Montréal, 5400, boulevard Gouin O, C-2095, H4J 1C5 Montreal, Quebec, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Leduc
authors.affiliation: Service de microbiologie médicale et infectiologie, hôpital du Sacré-Cœur de Montréal, 5400, boulevard Gouin O, C-2095, Montréal, H4J 1C5 Québec, Canada; Faculté de microbiologie, infectiologie et immunologie, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4 Québec, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Laflamme
authors.affiliation: Faculté de médecine, université de Montréal, 2900, boulevard Édouard-Montpetit, Montréal, H3T 1J4e Québec, Canada; Service de chirurgie orthopédique, hôpital du Sacré-Cœur de Montréal, 5400, boulevard Gouin O, C-2095, H4J 1C5 Montreal, Quebec, Canada. Electronic address: dominique_rouleau@yahoo.ca.
authors.forename: D M
authors.initials: DM
authors.lastname: Rouleau
mesh_terms: D000368:Aged; D060085:Coinfection / Q000175:diagnosis / Q000382:microbiology; D005260:Female; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis / Q000382:microbiology*; D006801:Humans; D007595:Joint Prosthesis / Q000382:microbiology*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures; D011425:Propionibacterium acnes / Q000302:isolation & purification*; D012008:Recurrence; D012189:Retrospective Studies; D012307:Risk Factors; D012785:Shoulder Joint / Q000382:microbiology
keywords: Implant infection; P. Acnes; Prosthesis infection