MOLECULAR VERSUS CONVENTIONAL MICROBIOLOGY IN MUSCULOSKELETAL INFECTION: NEAR-COMPLETE DETECTION WITH COMBINED TESTING BUT SIGNIFICANT DISCORDANCE

Aim Rapid pathogen identification is critical in musculoskeletal infection (MSKI). Conventional culture is limited by delayed turnaround and reduced sensitivity, while molecular diagnostics offer faster detection but uncertain concordance with culture. This study compared pathogen detection, concordance, and clinical utility of multiplex PCR-based molecular diagnostics versus conventional microbiology in MSKI. Methods A retrospective study was performed at a tertiary multidisciplinary bone infection unit. Consecutive patients with suspected MSKI who underwent both multiplex PCR-based diagnostics* and conventional microbiology were included. Primary outcomes were pathogen detection yield, overlap between modalities, pathogen concordance, resistance concordance, and discordance patterns. Results A total of 111 paired cases were analysed. Molecular diagnostics identified pathogens in 79.3% (88/111), while conventional culture was positive in 85.6% (95/111). Combined testing achieved pathogen detection in 99.1% (110/111), exceeding either modality alone. Both tests were positive in 73 cases, molecular-only positive in 15, culture-only positive in 22, and both negative in 1 case. Pathogen concordance was 55%, with 45% discordance. Resistance concordance was 56.8%, with 43.2% discordance. Discordance most commonly reflected additional organisms detected by molecular methods in polymicrobial infection, particularly anaerobes and low-virulence organisms, while culture additionally identified clinically relevant off-panel organisms. Discordance was more frequent in complex infections with prior antibiotic exposure, recurrent infection, and multiple previous surgical procedures. Conclusion Neither modality alone provided optimal microbiological yield in MSKI. Combined testing achieved near-complete pathogen detection (99.1%), but clinically significant discordance at pathogen and resistance levels was common. A complementary diagnostic strategy is recommended, combining rapid molecular detection for early decision-making with conventional microbiology for definitive pathogen identification and susceptibility testing. *Brand Name: BIOFIRE® Joint Infection Panel