Risk of mortality in Fusobacterium species bloodstream infection from a large Australian cohort

Background: Fusobacterium species are anaerobic Gram-negative bacilli which are uncommon causes of bloodstream infection (BSI). This genus commonly colonises the gastrointestinal tract and can result in significant morbidity. Methods: All blood cultures with growth of Fusobacterium species among residents of Queensland, Australia (population ≈ 5 million) were retrospectively identified over a 20-year period. Clinical, microbiological and outcome information was obtained from state-wide databases. Results: 377 incident Fusobacterium species BSI among 375 individuals for an age and sex-standardised incidence of 4.4 per million residents per year. Median age was 47 years (IQR, 24.9–65.8) and 156 (42%) incident episodes were in females. There was a bimodal frequency distribution with respect to age with peaks occurring around 20 and 65 years, respectively. The most identified source of infection was the abdominal (17%), followed by head and neck (12%). 8% of patients had a septic thrombus present, and 4% had an abscess associated with their BSI. Most isolates were F. nucleatum (142, 38%) and F. necrophorum (140, 37%). 9% of isolates were resistant to penicillin. Older age (aHR 1.02, 95% CI 1.01–1.05), healthcare-associated hospital onset (aHR 3.16, 95% CI 1.35–7.40), and Charlson Comorbidity index (aHR 1.20, 95% CI 1.06–1.35) were all associated with 30-day all cause case-fatality. Oropharyngeal source appeared to be a protective factor (P = 0.02). Conclusions: Fusobacterium species BSI results in significant morbidity and can cause death in vulnerable patient groups such as the elderly and those with malignancy. An identifiable oropharyngeal source identifies a favourable host.