title: Polymicrobial infections reduce the cure rate in prosthetic joint infections: outcome analysis with two-stage exchange and follow-up ≥two years.
abstract: Prosthetic joint infections (PJI) are a serious and challenging complication after total joint arthroplasty. According to the literature, most PJI are monomicrobial infections caused by gram-positive cocci. The number of polymicrobial PJI might be underrepresented in the literature and only limited data are available regarding the outcome of polymicrobial PJI. Our hypothesis was that polymicrobial PJI are associated with a reduced cure rate compared with monomicrobial PJI.
  
  
  
  Routine clinical data were collected and analysed retrospectively as anonymised, aggregated data. A total of 77 consecutive patients with 77 confirmed PJI and proven infectious organism of the hip and knee joint treated within a two-stage exchange concept and a follow-up ≥ two years were investigated. Detection of the infectious organism was based on multiple microbiological cultures taken intra-operatively. Superficial wound swabs or swabs from sinus tracts were not taken into account. Data were grouped into polymicrobial and monomicrobial PJI. The main outcome variable was "definitively free of infection after two years" as published. Second, we considered several variables as potential confounders or as risk factors.
  
  
  
  A total of 42 men and 35 women with 46 infected total hip arthroplasties and 31 infected total knee arthroplasties were evaluated. In 37 (46.6 %) of our 77 patients a polymicrobial PJI could be detected. We found a significant association between polymicrobial PJI and the outcome parameter definitively free of infection after two years with an odds ratio (OR) of 0.3 [95 % confidence interval (CI) 0.1-1.0]. The rate of patients graded as definitively free of infection after two years was 67.6 % for polymicrobial infections vs. 87.5 % for monomicrobial infections. The American Society of Anesthesiologists (ASA) score (OR 0.4, 95 % CI 0.2-1.0, p = 0.062) was identified as a borderline significant covariable.
  
  
  
  Our data suggest that polymicrobial PJI might be underrepresented in the current literature. Additionally, the presence of multiple infectious organisms is associated with a reduced rate after two years with 67.6 vs 87.5 % for monomicrobial infections. Special attention and extra care should be considered for these patients.
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany. wimmer@uni-bonn.de.
authors.forename: Matthias D
authors.initials: MD
authors.lastname: Wimmer
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Max J
authors.initials: MJ
authors.lastname: Friedrich
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Randau
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Milena M
authors.initials: MM
authors.lastname: Ploeger
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Schmolders
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Andreas A
authors.initials: AA
authors.lastname: Strauss
authors.affiliation: Institute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany.
authors.forename: Gunnar T R
authors.initials: GT
authors.lastname: Hischebeth
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Pennekamp
authors.affiliation: Division of Sports Medicine & Department of Orthopedic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Vavken
authors.affiliation: Department of Orthopaedics and Trauma Surgery, University Hospital Bonn, Bonn, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Gravius
mesh_terms: D000368:Aged; D001168:Arthritis / Q000601:surgery; D019643:Arthroplasty, Replacement / Q000009:adverse effects*; D060085:Coinfection / Q000150:complications*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007595:Joint Prosthesis / Q000009:adverse effects; D007719:Knee Joint / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016459:Prosthesis-Related Infections / Q000601:surgery*; D012086:Reoperation; D012189:Retrospective Studies; D012307:Risk Factors
keywords: Arthroplasty; Infection; Polymicrobial; Prosthetic joint infection; Revision