Epidemiology of aneurysmal subarachnoid hemorrhage in Australia and New Zealand - Incidence and case fatality from the Australasian Cooperative Research on Subarachnoid Hemorrhage Study (ACROSS)

Background and Purpose-More data on the epidemiology of subarachnoid hemorr hage (SAH) are required to increase our understanding of etiology and preve ntion. This study sought to determine the incidence and case fatality of SA H from 4 prospective, population-based registers in Australia and New Zeala nd. Methods-We identified all cases of "aneurysmal" SAH from November 1995 to J une 1998 in Adelaide, Hobart, Perth (Australia), and Auckland (New Zealand) , a total population of approximately 2.8 million, using standard diagnosti c criteria and uniform community-wide surveillance and data extraction proc edures. Results-A total of 436 cases of SAH were registered, including 432 first-ev er events and 4 recurrent events. The mean age of cases was 57 years (range , 16 to 94 years), and 62% were female. From the 400 first-ever events regi stered over whole years, the crude annual incidence for the total populatio n was 8.1 per 100 000 (95% CI, 7.4, 9.0), with rates higher for females (9. 7; 95% CI, 8.6, 11.0) than for males (6.5; 95% CI, 5.5, 7.6). Age-specific rates showed a continuous upward trend with age, although the shape and str ength of this association differed between the sexes; Standardized annual i ncidence of SAH varied across centers, being highest in Auckland largely be cause of the high rate in Maori and Pacific people. The 28-day case fatalit y rate for the total population was 39% (95% CI, 34%, 44%), with little var iation in ratios across centers. Conclusions-There is variation in the incidence of SAH in Australia and New Zealand, but the rates are consistently higher for females. A monotonic in crease in incidence with age suggests that exposures with cumulative effect s and long induction times may be less relevant in the etiology of SAH.