How is the microbial diagnosis of bacterial vertebral osteomyelitis performed? An 11-year retrospective study

Vertebral osteomyelitis (VOM) is often diagnosed with delays, resulting in poorer outcomes. Microbial documentation is particularly challenging and obtained using blood cultures (BCs) and vertebral biopsies (VBs; CT-guided or surgical). We retrospectively analysed VOM cases in a tertiary reference centre between 2004 and 2015, focusing on how and how quickly microbiological diagnosis was performed. Among 220 VOM, 88.2% had documentation, including Gram-positive cocci (GPC) (70.6%), Gram-negative rods (GNR) (9.3%), anaerobes (3.6%), polybacterial infections (6.7%) and tuberculosis (9.8%). BCs were performed in 98.2% and positive in 59.3%, identifying most GPC (80.3%) and half of GNR (54.6%). VBs were performed in fewer cases (37.7%), but were more frequently positive (68.8% for CT-guided and 81.0% for surgical biopsies). They documented all anaerobes (100.0%), most M. tuberculosis (84.2%) and polybacterial infections (76.9%), and GNR (45.4%). Extra-vertebral samples highly contributed to tuberculosis diagnosis (52.6%, and 15.8% as the only positive sample). Documentations most often followed radiological diagnosis (53.4%). They were obtained earlier by BCs than by VB after first clinical symptoms (median of 14 versus 51 days). Antibiotic treatments were mostly initiated after samplings (88.0%). BCs allow the documentation of most VOM and should be performed without delay in case of clinical or radiological suspicion; however, they may miss 1 out of 5 GPC and 1 out of 2 GNR. VBs have a higher positivity rate and should be rapidly performed if negative BCs. It is likely that delayed and missed diagnoses result from the insufficient use of VB.