Quantitative Real-Time Polymerase Chain Reaction May Serve as a Useful Adjunct to Conventional Culture in The Detection of Cutibacterium acnes in the Glenohumeral Joint: A Study of 100 Consecutive Patients

Document Type : RESEARCH PAPER


Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA



Objectives: Synovial fluid or tissue culture is the current gold standard for diagnosis of infection, but 
Cutibacterium acnes (C. acnes) is a frequent cause of shoulder PJI and is a notoriously fastidious 
organism. The purpose of this study was to compare quantitative real-time polymerase chain reaction 
(qRT-PCR) to standard culture as a more rapid, sensitive means of identifying C. acnes from the 
glenohumeral joint. We hypothesized that qRT-PCR would be more effective than standard culture at 
identifying C. acnes and would have greater sensitivity and specificity for detecting infection.
Methods: This was a prospective observational study with 100 consecutive patients undergoing arthroscopic or 
open shoulder surgery with known positive and negative controls. Intraoperatively, synovial fluid and tissue was 
obtained for C. acnes qRT-PCR and results were blinded to the gold standard microbiology cultures.
Results: Clinical review demonstrated 3 patients (3%) with positive cultures, none of which were positive for C. 
acnes. Of the samples tested by the C. acnes qRT-PCR standard curve, 12.2% of tissue samples and 4.5% of fluid 
samples were positive. Culture sensitivity was 60.0%, specificity was 100.0%, PPV was 100.0%, and NPV was 
97.9%. C. acnes qRT-PCR standard curve sensitivity, specificity, PPV, and NPV was 60.0%, 90.3%, 25.0%, and 
97.7% respectively for tissue specimens and 0%, 95.2%, 0%, and 95.2% respectively, for fluid specimens. For 
combination of culture and tissue qRT-PCR, the sensitivity, specificity, PPV and NPV was 100%, 90.3%, 35.7%, 
and 100%, respectively.
Conclusion: We report that qRT-PCR for C. acnes identified the organism more frequently than conventional 
culture. While these findings demonstrate the potential utility of qRT-PCR, the likelihood of false positive results of 
qRT-PCR should be considered. Thus, qRT-PCR may be useful as an adjuvant to current gold standard workup of 
synovial fluid or tissue culture for the diagnosis of infection.
 Level of evidence: II


Main Subjects