FOCUS ON MRSA/SA SSTI ASSAY FAILURE IN PROSTHETIC JOINT. Institute of Microbiology, Lille University Hospital, F Lille, France

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1 JCM Accepted Manuscript Posted Online 16 November 2016 J. Clin. Microbiol. doi: /jcm Copyright 2016, American Society for Microbiology. All Rights Reserved. FOCUS ON MRSA/SA SSTI ASSAY FAILURE IN PROSTHETIC JOINT INFECTIONS: 213 CONSECUTIVE PATIENTS LATER 1 2 Marie Titécat 1,5, Frédéric Wallet 1,5, Olivier Robineau 2,5, Michel Valette 2, Henri Migaud 3,4,5, Eric Senneville 2,4,5, Caroline Loïez 1, Institute of Microbiology, Lille University Hospital, F Lille, France 2 University Department of Infectious Diseases, Gustave Dron Hospital, F Tourcoing, France 3 Orthopaedic Department, Lille University Hospital, F Lille, France 4 Northwest Reference Center for Osteoarticular Infections (CRIOAC-G4 Lille-Tourcoing), F Lille, France 5 University of Lille, F Lille, France Running title: MRSA/SA SSTI assay failure in prosthetic joint infections Corresponding author: Marie TITECAT Laboratoire de Bactériologie-Hygiène Centre de Biologie Pathologie F Lille Cedex, France marie.titecat@chru-lille.fr 19 Key Words: Prosthetic joint infection, meca, vancomycin, Staphylococcus addresses of coauthors: frederic.wallet@chru-lille.fr olivier.robineau82@gmail.com mvalette@ch-tourcoing.fr henri.migaud@chru-lille.fr esenneville@ch-tourcoing.fr caroline.loiez@chru-lille.fr

2 In prosthetic joint infection (PJI) cases (1), rapid detection of methicillin-resistant staphylococci (MRS) is the key to avoid the use of broad-spectrum antimicrobials such as vancomycin. Indeed, vancomycin use is associated with a risk of renal impairment, a lesser efficacy against methicillin-susceptible strains when compared with beta-lactams (2) and a negative ecological impact. In these regards, the Xpert MRSA/SA SSTI assay (Cepheid, Sunnyvale, CA, USA) appears as a potential useful tool. It enables the detection of the genetic support of methicillin resistance, the meca gene, directly in intra-operative samples (IOS) in less than one hour (3). In our center, the test has been routinely used for the last four years in order to early stop the anti-mrs antibiotic in those patients managed for PJI and having a negative result for the detection of the meca gene in surgical samples. For each patient, 3 IOS were taken to perform both standard culture and molecular testing before any antimicrobial therapy. These three samples were also kept for prolonged culture (15 days) in Rosenow s enrichment broth (4, 5). The criteria for a microbiological infection were: the same coagulase negative Staphylococcus (CoNS) species related to the same antimicrobial pattern found in culture in at least 2 samples and/or a S. aureus strain found in culture in at least 1 sample. Methicillin susceptibility was assessed by using Vitek2 AST cards (biomérieux, Marcy l Etoile, France). Oxacillin and cefoxitin results issued from the automated system were interpreted according to the CA-SFM recommendations ( A cefoxitin disk was also tested in case of discrepancy. Among the 213 consecutive patients studied (118 hip, 82 knee and 13 shoulder prosthesis), culture was correlated to the molecular detection of a MRS in 186 cases (87.3%). Overall sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were 56%, 93%, 58% and 92% respectively. Xpert failed to detect a resistant strain in 14 out of 213 patients (6.6%) which were examined carefully owing to a high risk of clinical failure. Eight of these false negative patients were positive with a single MR coagulase negative staphylococcus

3 (MRCoNS) strain, either in standard or in enriched medium, which could be considered as a contamination. The six remaining cases were positive in culture with an MRCoNS (patients 1 to 5) or a MRSA (methicillin-resistant Staphylococcus aureus) (patient 6) PJI (Table 1). Xpert failed to diagnose one patient (patient 1) because of a late amplification (C t = 39.1) interpreted as negative by the software. Two other patients (patients 3 and 5) had a polymicrobial infection. Patients 2, 4 and 6 were infected by MRSE (MR Staphylococcus epidermidis) and MRSA small colony variants respectively. None of these false negative patients had a microbiological relapse. In the light of these data, Se, Sp, PPV and NPV values moved to 75%, 93%, 58% and 97% respectively. Xpert is an easy PCR method we turned away in favor of bone and joint infections diagnosis and rapid antimicrobial adjustment. High performances of the test were described in osteoarticular infections (3), and chronic PJI (5), but they were recently unbalanced by poor sensitivity results (36%) in case of MRCoNS infection (6). These points were examined here on an extended cohort of 213 patients. A focus on false negative cases revealed different kind of risk factors such as (i) MRCoNS infections, (ii) high C t value related to low inoculum, (iii) polymicrobial infections and (iiii) small colony variant infections. Furthermore, comparison was made between PCR and culture, but culture remains an imperfect gold standard that must be interpreted according to the patients' medical history (e.g. 8/14 contaminations). In conclusion, our results confirm the high NPV of Xpert which makes it a useful tool in an attempt to reduce vancomycin use in PJI AKNOWLEDGEMENTS We thank Philippe Choisy for technical assistance and Pr Mecos for critically reading the manuscript.

4 CONFLICT OF INTEREST E. Senneville: speaker for Cepheid All other authors: none to disclose. 81

5 REFERENCES 1. Zimmerli W, Trampuz A, Ochsner PE Prosthetic-joint infections. N Engl J Med 351: Kim SH, Kim KH, Kim HB, Kim NJ, Kim EC, Oh M, Choe KW Outcome of Vancomycin Treatment in Patients with Methicillin-Susceptible Staphylococcus aureus Bacteremia. Antimicrob Agents Chemother 52: Dubouix-Bourandy A, Ladoucette A de, Pietri V, Mehdi N, Benzaquen D, Guinand R, Gandois JM Direct Detection of Staphylococcus Osteoarticular Infections by Use of Xpert MRSA/SA SSTI Real-Time PCR. J Clin Microbiol 49: Senneville E, Savage C, Nallet I, Yazdanpanah Y, Giraud F, Migaud H, Dubreuil L, Courcol R, Mouton Y Improved aero-anaerobe recovery from infected prosthetic joint samples taken from 72 patients and collected intraoperatively in Rosenow s broth. Acta Orthopaedica 77: Titécat M, Loïez C, Senneville E, Wallet F, Dezèque H, Legout L, Migaud H, Courcol RJ Evaluation of rapid meca gene detection versus standard culture in staphylococcal chronic prosthetic joint infections. Diagnostic Microbiology and Infectious Disease 73: Lourtet-Hascoëtt J, Bicart-See A, Félicé MP, Giordano G, Bonnet E Is Xpert MRSA/SA SSTI real-time PCR a reliable tool for fast detection of methicillin-resistant

6 coagulase-negative staphylococci in periprosthetic joint infections? Diagnostic Microbiology and Infectious Disease 83:59-62.

7 TABLE 1: Characteristics of the 6 patients negative for meca detection INTRA- OPERATIVE SAMPLES (No. of days for positive culture) Patient Sex Culture medium IOS 1 IOS 2 IOS 3 meca detection (C t) 1 M 2 F 3 M 4 F Standard MRSE (day 3) Sterile Sterile Enriched broths MRSE (day 3) MRSE (day 3) MRSE (day 3) Standard Sterile Sterile Sterile Enriched broths MRSE (day 4) MRSE (day 4) Sterile Standard MS S. pettenkofferi MS S. pettenkofferi + MR S. capitis Sterile (day 4) (day 4) Enriched broths MR S. hominis (day 2) MS S. caprae + MR S. capitis MS S. caprae + Bacillus simplex (day 2) (day 2) Standard Sterile MRSE (day 5) Sterile Enriched broths Sterile MRSE (day 5) MRSE (day 6) Negative (39.1) 5 F 6 M Standard Sterile MRSE (day 2) Lactobacillus rhamnosus (day 5) Enriched broths Lactobacillus rhamnosus (day 3) MRSE (day 2) Lactobacillus rhamnosus (day 3) Standard Sterile Sterile MRSA (day4) Enriched broths MRSA (day 5) MRSA (day 6) MRSA (day4) Abbreviations: MRSE, Meticillin Resistant Staphylococcus epidermidis; MRSA, Meticillin Resistant Staphylococcus aureus; MR, Meticillin Resistant; MS, Meticillin Susceptible; C t, cycle threshold