JBJI Journal of Bone and Joint Infection JBJI J. Bone Joint Infect. 2206-3552 Ivyspring Göttingen, Germany 10.7150/jbji.31312 Is Gram staining still useful in prosthetic joint infections? Wouthuyzen-Bakker Marjan 1 Shohat Noam 2 3 Sebillotte Marine 4 Arvieux Cédric 4 5 Parvizi Javad 2 Soriano Alex 6 Department of Medical Microbiology and Infection Prevention, University of Groningen, University Medical Center Groningen, the Netherlands. Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, United States. Department of Orthopaedic Surgery, Tel Aviv University, Tel Aviv, Israel. Department of Infectious Diseases and Intensive Care Medicine, Rennes University Hospital, Rennes, France. Great West Reference centers for Complex Bone and Joint Infections (CRIOGO), France. Service of Infectious Diseases, Hospital Clínic, University of Barcelona, Barcelona, Spain. 29 01 2019 4 2 56 59 Copyright: © 2019 Marjan Wouthuyzen-Bakker et al. 2019 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://jbji.copernicus.org/articles/4/56/2019/jbji-4-56-2019.html The full text article is available as a PDF file from https://jbji.copernicus.org/articles/4/56/2019/jbji-4-56-2019.pdf

<p class="p p-first" id="__p2"><strong>Introduction</strong>: <em>Staphylococcus aureus</em> is an independent risk factor for DAIR failure in patients with a late acute prosthetic joint infection (PJI). Therefore, identifying the causative microorganism in an acute setting may help to decide if revision surgery should be chosen as a first surgical approach in patients with additional risk factors for DAIR failure. The aim of our study was to determine the sensitivity of Gram staining in late acute <em>S. aureus</em> PJI.</p><p id="__p3"><strong>Material and methods</strong>: We retrospectively evaluated all consecutive patients between 2005-2015 who were diagnosed with late acute PJI due to <em>S. aureus</em>. Late acute PJI was defined as the development of acute symptoms and signs of PJI, at least three months after the index surgery. Symptoms existing for more than three weeks were excluded from the analysis. Gram staining was evaluated solely for synovial fluid.</p><p id="__p4"><strong>Results</strong>: A total of 52 cases were included in the analysis. Gram staining was positive with Gram positive cocci in clusters in 31 cases (59.6%). Patients with a C-reactive protein (CRP) &gt; 150 mg/L at clinical presentation had a significantly higher rate of a positive Gram stain (30/39, 77%) compared to patients with a CRP ≤ 150 mg/L (4/10, 40%) (p=0.02). A positive Gram stain was not related to a higher failure rate (60.6% versus 57.9%, p 0.85).</p><p class="p p-last" id="__p5"><strong>Conclusion</strong>: Gram staining may be a useful diagnostic tool in late acute PJI to identify <em>S. aureus</em> PJI. Whether a positive Gram stain should lead to revision surgery instead of DAIR should be determined per individual case.</p>

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