Incidence of subarachnoid haemorrhage: an Australian national hospital morbidity database analysis.

Incidences of subarachnoid haemorrhage (SAH) in Australia have been reported in regional studies with variable rates. We investigated the national SAH rate and evaluated the trend over the 10 years from 1998 to 2008. The crude SAH incidence, not related to trauma or arteriovenous malformation, was estimated at 10.3 cases per 100,000 person-years (95% confidence interval [CI]: 10.2-10.4). Females have a higher incidence of SAH (12.5 cases per 100,000; 95% CI: 12.3-12.8) compared to males (8.0 cases per 100,000; 95% CI: 7.8-8.3), with age-adjusted incidence increases with increasing age for both sexes. Less than 10% of SAH occurred in the first three decades of life. The peak age group for patients to experience SAH was between 45 years and 64 years, accounting for almost 45% of the overall annual SAH admissions. Aneurysms located in the anterior circulation were a more common source of rupture compared to those located in the posterior circulation (rate ratio 3.9; 95% CI: 3.6-4.2). Contrary to contemporary observations in the literature, we did not observe a decline in the incidence of SAH during this specified study period.