AUTOMATED MULTIPLEX PCR FOR IDENTIFYING THE CAUSING PATHOGEN IN SEPTIC ARTHRITIS

Aim Septic arthritis (SA) in adults can lead to serious complications if not diagnosed promptly. Conventional synovial fluid culture (CC) remains the gold standard for identifying the causing microorganism but is time-consuming and often insensitive, particularly in patients receiving antimicrobial therapy. This study aimed to evaluate the diagnostic performance of a novel automated multiplex PCR (mPCR) system and compared it to conventional culture (CC) in adults with suspected acute native joint infections. Method In this retrospective single-centre study, adult patients with suspected SA (February 2023-May 2024) were included. Diagnosis was based on institutional criteria incorporating clinical signs, synovial fluid cytological, microbiology, and histology. Agreement between mpCR and CC was assessed using overall percentage agreement and Cohen's Kappa coefficient. Diagnostic performance metrics were calculated for mPCR, CC, and their combined use. Results Of 143 included patients, 96 (67%) were diagnosed with SA. When considering mPCR-specific microorganisms, mPCR identified 13 additional microorganisms compared to CC. Nine of these (9/13) were diagnosed with SA and six of these (6/9, 67%) were on antibiotics prior to aspiration. Overall agreement between mPCR and CC was 91%, with a positive agreement of 100%, negative agreement of 88% and a Cohen's Kappa coefficient of 0.780. Considering all microorganisms (including off-panel organisms), the overall agreement was 89%, the positive agreement 92%, the negative agreement 88%, and the Cohen's Kappa 0.735. The mPCR demonstrated a sensitivity of 45% and specificity of 89%, while conventional culture showed a sensitivity of 40% and specificity of 100%. No significant difference in performance was observed between the two methods (p = 0.183). Moreover, the combined use (mPCR + CC) yielded a sensitivity of 48% and specificity of 89% (AUC = 0.686). Conclusions The novel automated mPCR system demonstrated a diagnostic performance similar to that of conventional synovial fluid culture, offering the added benefit of a quicker turnaround time, which can be crucial for patient care. Its use is especially evident in patients who have received prior antibiotic treatment, where conventional cultures may be less reliable.