Evaluating factors influencing mortality, neurological morbidity and length of stay in adults admitted with community-onset brain abscess in a UK tertiary referral centre

• This article describes a retrospective review of 60 cases of community-onset brain abscess in adults. We identify key risk factors, as well as outcome data, including use of the modified Rankin Scale, a widely accepted measure of neurological disability and dependence, which adds significantly to the existing literature in brain abscess, in whom morbidity is rarely objectively measured. This is particularly crucial in this rare condition, to ensure that follow up and support is available appropriately to patients with adverse outcomes following brain abscess. We secondarily analyse length of stay, neurological sequelae (such as resultant epilepsy) and mortality data. This is the largest UK-based cohort thus far described, and given the impact of brain abscess, we feel this is an important study to share. Despite advances in diagnostics and therapeutics, morbidity and mortality associated with brain abscess remains high. Until recently no evidence-based guidelines existed, resulting in heterogeneous practice. In this study we explore the impact of host, pathogen and therapy-related factors on clinical outcomes. We retrospectively reviewed adult patients with community-onset brain abscess from October 2016 to April 2020 using hospital databases. Clinical, radiological, biochemical, microbiological, and surgical data was collected. Primary outcome was the 6 month modified Rankin Scale (mRS), secondary outcomes included length of hospital stay (LOS), neurological sequelae, and 1-year mortality. Multivariate logistic regression was used to analyse factors influencing recovery and neurological sequelae; and multivariate Cox regression for LOS. Sixty adults with brain abscess (median age 57 years; 63 % male) were identified. Forty-eight patients (80 %) had a solitary abscess, most commonly in the frontal lobe. A causative organism was identified in 49 of 54 cases (91 %) where samples were collected, with Streptococcus milleri group the most common organism. Median duration of intravenous and oral therapy was 21 and 28 days respectively. Forty-three patients had an mRS of ≤ 2 (slight disability or better) at 6 months, with CRP > 6 mg/l on admission associated with poor outcome (mRS > 2) (p = 0.036). Eight patients (13 %) died within one year. Age > 60 years (p = 0.001), CRP > 6 mg/l (p = 0.048) and prolonged intravenous therapy (>6 weeks) (p = 0.001) were all associated with extended LOS. Seizures on admission (p = 0.017) or presence of risk factors (p = 0.032) were associated with neurological sequelae at 6 months. This study reveals that a complex interaction of factors related to host, pathogen and therapy impacts clinical outcome in patients with brain abscess. While mortality and LOS are well described in previous literature, analysis of the mRS here adds to our understanding of morbidity following a diagnosis of brain abscess.