Epidemiology of Aneurysmal Subarachnoid Hemorrhage in Australia and New Zealand

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Abstract
Background and Purpose —More data on the epidemiology of subarachnoid hemorrhage (SAH) are required to increase our understanding of etiology and prevention. This study sought to determine the incidence and case fatality of SAH from 4 prospective, population-based registers in Australia and New Zealand. Methods —We identified all cases of “aneurysmal” SAH from November 1995 to June 1998 in Adelaide, Hobart, Perth (Australia), and Auckland (New Zealand), a total population of approximately 2.8 million, using standard diagnostic criteria and uniform community-wide surveillance and data extraction procedures. Results —A total of 436 cases of SAH were registered, including 432 first-ever 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 registered over whole years, the crude annual incidence for the total population 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 strength of this association differed between the sexes. Standardized annual incidence of SAH varied across centers, being highest in Auckland largely because of the high rate in Maori and Pacific people. The 28-day case fatality rate for the total population was 39% (95% CI, 34%, 44%), with little variation 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 increase in incidence with age suggests that exposures with cumulative effects and long induction times may be less relevant in the etiology of SAH.