Adult intracranial bacterial abscesses in Ireland (2010-2021) associated with a low mortality. Luck of the Irish?

To describe the epidemiology, microbiology and clinical outcomes of adult patients (aged ≥16 years) diagnosed with bacterial intracranial abscesses in the Republic of Ireland.

A 12-year retrospective analysis from 2010 to 2021 was conducted in the Republic of Ireland's two neurosurgical centres. Radiological, microbiological, and medical records of adult patients with confirmed intracranial abscesses were analysed.

Of 192 patients, 127 were male (66.2%); mean age at diagnosis was 54 years (SD = 10.5). Community-acquisition occurred in 183 (95.3%) cases. The highest annual case number was recorded in 2020 (n = 32). A preceding or concurrent sinusitis, mastoiditis, or dental infection was identified in 39.1% (n = 75), prior neurosurgical procedure in 14.6% (n = 28), and infective endocarditis in 14.6% (n = 28). Solitary abscesses were present in 82.3% (n = 158), with frontal lobe abscesses predominating (38.6% [61/158]). Neurosurgical drainage was performed in 90.6% (n = 174). A single organism was cultured in 84 patients; Streptococcus intermedius most commonly (n = 35). Polymicrobial infection was identified in 27.9% (n = 48), culturing S. intermedius (n = 16), anaerobes (n = 33) and Gram-negative organisms. Of 40 culture-negative specimens, an organism was detected in 10 cases by 16S rRNA gene PCR. In-hospital mortality was 3.1%.

This first national cross-site study on intracranial abscess in the Republic of Ireland highlights the predominance of S. intermedius, reflecting a shift from Staphylococcus aureus. In-hospital mortality appears lower than previously reported internationally underscoring the need for continued surveillance and robust outcome data collection.