Impact of Targeted PCR Testing Compared to Conventional Cultures on Diagnostic Yield in Pediatric Patients with Septic Arthritis

Corresponding Author Diana Nguyen, Diana.Nguyen@bcm.edu Funding None. Conflict(s) of Interest The authors declare no conflicts or financial interest in any product or service mentioned in the manuscript, including grants, equipment, medications, employment, gifts, and honoraria. Background Many patients with septic arthritis receive antibiotics prior to synovial fluid sampling, which often result in negative culture results. In addition, organisms such as Kingella kingae are difficult to grow in cultures. We hypothesized that a laboratory developed PCR assay that targets typical bone and joint pathogens, such as Staphylococcus aureus and K. kingae, can assist with diagnosis and promote antimicrobial stewardship. The objective of our study was to compare the diagnostic yield and time to pathogen identification between a laboratory developed PCR assay and standard culture techniques for pediatric patients with septic arthritis. Methods Pediatric patients that had both an in-house PCR test and culture of synovial joint fluid ordered from 11/1/2019 through 9/30/2024 were eligible for inclusion. Patients were included in the analysis if either test was positive for the following pathogens: S. aureus, Streptococcus pneumoniae, Streptococcus pyogenes, K. kingae, and Neiseria meningitidis. Variables collected included time of test and culture collection, results, and timing of results. Two-sided t-tests were used to compare continuous variables. Results Three-hundred twenty five patients were screened for inclusion; 117 (36%) had a positive PCR test result and 53 (16.3%) had a positive culture result. Median time to identification was 27.3 hours (range 6-99.4 hours) and 44.3 hours (range 34.6-121.5 hours) for PCR and culture results, respectively (p=.002). Median time to susceptibility results for S. aureus from culture was 70.1 hours (range 21.6-149.4 hours) compared to 28.2 hours for PCR (p<.00001).Fifty-six (47.9%) patients with a positive PCR result had bacteria identified by PCR but not in culture; 29 (51.2%) PCR tests were positive for K. kingae. Four patients (7.1%) had a negative PCR but a culture positive for methicillin-susceptible S. aureus. Conclusion PCR testing resulted in a significantly faster time to pathogen identification compared to synovial fluid cultures and allowed for identification of fastidious organisms such as K. kingae. Targeted PCR testing may be a useful antimicrobial stewardship tool by allowing narrowing of antibiotic regimens.