Aim

Treatment of chronic prosthetic joint infection (PJI) combines exchange arthroplasty and effective antibiotic therapy. Staphylococci are the most frequent microorganism isolated in PJIs, with resistance to methicillin found in 15–50% of the cases. Data from randomized trials on treatment of methicillin-resistant staphylococci are lacking and the choice of antibiotic(s) and recommendations vary according to authors. To date, combination therapy including vancomycin is the treatment of choice.

Minocycline, a cyclin antibiotic, is naturally effective against methicillin-resistant staphylococci. We use this antibiotic since many years in combination with vancomycin for the treatment of multi-drug resistant staphylococcal bone and joint infections.

The aim of this study is to analyze the outcome of patients treated with combination antibiotic therapy including minocycline for the treatment of chronic methicillin-resistant staphylococcal PJI.

The diagnosis of prosthetic joint infections (PJI) represents a critical challenge for orthopedic surgeons and infectious disease specialists. The diagnosis of PJI is often delayed because non-invasive assays lack sensitivity and specificity. A novel multiplex immunoassay detecting antibodies against Staphylococci, Propionibacteria and Streptococcus agalactiae was developed and its performance evaluated in a prospective, multicenter, non-interventional study.

The Luminex-based assay measures serum IgG against a proprietary panel of recombinant purified antigens from Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus lugdunensis, Streptococcus agalactiae and Propionibacterium acnes. Patients undergoing revision arthroplasty were included over a 2-year period (from 2012 up to 2014) in two French reference centers in compliance with IRB and French regulations. PJI cases were defined microbiologically (≥2 intraoperative samples yielding the same microorganism) for confrontation of microbiological and immunoassay data.

455 patients were eligible for study analyses. 149 patients (32.7%) were found to be infected. Among the most frequent infecting species recovered were S. aureus (30%), S. epidermidis (26%), P. acnes (9%), S. lugdunensis (6%), and S. agalactiae (4%). The sensitivity and specificity values of the test were, respectively, 75.9% (63/83) and 82.2% (180/219) for staphylococci (S. aureus, S. epidermidis, S. lugdunensis), 38.5% (5/13) and 81.9% (190/232) for P. acnes, and 66.7% (4/6) and 92.4% (208/225) for S. agalactiae. Interestingly, all cases (9/9) involving S. lugdunensis were detected by the test and the sensitivity for S. epidermidis reached 79.4% in patients more than three months after joint replacement. In a similar fashion, 89.5% (17/19) in the subpopulation with elevated inflammatory markers (ESR>30 and CRP>10).

The assay correctly identified 67% of the microbiologically positive patients that were negative by ESR or CRP screening.

This novel multiplex serological test allows the rapid and non-invasive diagnosis of the most frequent PJI pathogens, showing a good correlation with microbiological culture. and appears to be a new promising tool in the management of PJI, adding sensitivity to the current serological assays and enhancing the management of patients with pauci-inflammatory PJI.

Purpose of the study: Plurimicrobial infections account for 4 to37% of all infections of total hip arthroplasties (THA). According to data in the literature, they are the source of failure, contraindicating one-phase replacement procedures. The purpose of our study was to evaluate the results of our management practices in this group of patients and also to identify factors of risk associated with multimicrobial infection.

Material and methods: A prospective study included 116 patients with an infected THA from November 2002 to December 2006. Sixteen patients (13.8%), mean age 68±12.7 years had a plurimicrobial infection defined by having at last two interoperative bacteriological samples positive for two or more germs. Surgical treatment consisted in a single-phase replacement in seven cases, a two-phase replacement in seven, resection of the head and neck in one, and wash-out resection in one. Mean duration of the antibiotic therapy ws 91±6 days, including 46±14 days intravenously. Anaerobic germs were isolated more commonly in plurimicrobial infections than monomicrobial infections (50% versus 11%). Patients were assessed with prospectively collected data. Mean follow-up was 34±13 months, with none lost to follow-up. The main outcome was apparent cure rate of the initial infection at minimum two years follow-up, defined by the absence of clinical, biological and radiographic signs of infection, and absence of death attributable to infection or its treatment. If infection was suspected, a hip puncture or intraoperative samples confirmed the relapse (same germs) or reinfection (different germs).

Results: The cure rate was 100% for plurimicrobial infections and 97% for monomicrobial infections. There were however four reinfections in the monomicrobial group. In this series, the risk factor statistically associated with plurimicrobial infections was the presence of a fistula with an odds ratio of 5.4.

Discussion: A larger number of patients would probably enable identification of other risk factors associated with plurimicrobial infections.

Conclusion: The cure rate of plurimicrobial infections was higher than reported in the literature but for a small group of patients. The presence of a fistula was strongly associated with these plurimicrobial infections.