ANALYZING REAL-WORLD UTILITY OF A MULTIPLEX-PCR FOR THE IDENTIFICATION OF A PATHOGEN CAUSING SEPTIC ARTHRITIS

Aim This study evaluated the real-world use of the a commercial multiplex-PCR panel (1) as an adjunct to standard microbiological processes focusing on the review of discordant molecular and culture results. Method We retrospectively reviewed all cases where a multiplex-PCR panel was performed on a clinical specimen in our laboratory during 2024. Discordant results were analysed by two independent clinicians who made a clinical judgement based on available microbiology and details from the electronic medical record. Results There were 329 samples from 307 separate patients where a multiplex-PCR and bacterial culture was performed on a clinical specimen collected between 1 st January and 31 st December 2024. 279 (85%) were negative by culture and PCR, 27 (8%) were positive for the same species by culture and PCR. 13 (48%) of the positive culture and PCR concordant cases had organisms seen on the gram stain. There were 23 discordant results (7%), of which 5 were culture positive and PCR negative, 17 were culture negative and PCR positive and 1 was positive for different isolates on culture and PCR (likely polymicrobial infection). Of the culture negative and PCR positive cases, only 1 (6%) had organisms seen on the gram stain. In cases with culture positive and PCR negative discordance, the most common reason was due to the isolate not being present on PCR panel (n=3). In cases with culture negative and PCR discordance, the common reasons were due to infection with fastidious organisms (n=3) and prior antibiotic exposure (n=12). Conclusions Joint fluid multiplex-PCR may be a useful adjunctive tool for diagnosis of septic arthritis but is expensive. It may help improve identification of a pathogen particularly for suspected fastidious organisms or if antibiotics have been administered prior to specimen collection. Unnecessary use can be limited by only proceeding with PCR if the gram stain is negative. Further research is required to identify cases where it may be most clinically useful to help manage resources and ensure good diagnostic stewardship. Acknowledgements The authors state that there are no conflicts of interest to disclose.