Temporal trends in incidence, clinical characteristics and outcomes of pyogenic vertebral osteomyelitis in Southern Denmark from 2009 to 2022: a retrospective population-based cohort study

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Pyogenic vertebral osteomyelitis (PVO) is a severe infection with increasing incidence. We aimed to describe long-term population-based temporal trends in incidence, clinical presentation, diagnostic approaches, microbiology, and outcomes. We conducted a retrospective population-based cohort study including 1,017 adults with multidisciplinary team–verified PVO diagnosed at a tertiary infectious diseases referral centre in the Region of Southern Denmark between 2009 and 2022. Incidence rates (IRs) per 100,000 person-years (PY) were calculated using regional population data and compared across three calendar periods (2009–2013, 2014–2018, 2019–2022). Temporal changes in clinical characteristics, microbiology, diagnostic strategies, and outcomes were assessed. In total, 1,017 patients were included. The crude IR increased from 4.7 per 100,000 PY in 2009–2013 to 11.0 in 2019–2022, with the largest increase among patients aged ≥70 years. Mean age and comorbidity burden rose over time. Pain was common, fever was often absent, and neurological deficits occurred in 33.5% (n = 341). Postsurgical infection was the most frequent primary focus, and concomitant endocarditis occurred in 8.3% (n = 84). A microbiological diagnosis was established in 64.8% (n = 635) of cases, most commonly Staphylococcus aureus. Use of Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography ([18F]FDG-PET/CT) increased over time. Median hospital stay remained 33 days. One-year mortality increased from 9.5% to 18.2%, while relapse declined, resulting in a stable composite risk of death or relapse (20.7%). The incidence of PVO increased markedly from 2009 to 2022, predominantly in older patients with comorbidities. Despite improved diagnostics, microbiologically-negative cases remain frequent. Mortality remained high and increased over time. The incidence of pyogenic vertebral osteomyelitis increased substantially over the 14-year study period, particularly in an ageing and increasingly comorbid population. Patients presented with signs of more advanced disease despite shorter symptom duration, while the persistently high proportion of microbiologically negative cases underscored ongoing diagnostic challenges. Sustained mortality and long-term pain highlight the considerable burden of PVO and the need for improved diagnostic pathways, risk stratification, and treatment strategies.