Incidence of the Major Stroke Subtypes: Initial Findings From the North East Melbourne Stroke Incidence Study (NEMESIS)

Abstract

Background and Purpose — Population-based stroke incidence studies are the only accurate way to determine the number of strokes that occur in a given society. Because the major stroke subtypes have different patterns of incidence and outcome, information on the natural history of stroke subtypes is essential. The purpose of the present study was to determine the incidence and case-fatality rate of the major stroke subtypes in a geographically defined region of Melbourne, Australia. Methods — All suspected strokes that occurred among 133 816 residents of suburbs north and east of Melbourne, Australia, during a 12-month period of 1996 and 1997 were identified and assessed. Multiple overlapping sources were used to ascertain cases, and standard criteria for stroke and case-fatality were used. Stroke subtypes were defined by CT, MRI, and autopsy. Results — Three hundred eighty-one strokes occurred among 353 persons during the study period, with 276 (72%) being first-ever-in-a-lifetime strokes. Of these, 72.5% (95% CI 67.2% to 77.7%) were cerebral infarction, 14.5% (95% CI 10.3% to 18.6%) were intracerebral hemorrhage, 4.3% (95% CI 1.9% to 6.8%) were subarachnoid hemorrhage, and 8.7% (95% CI 5.4% to 12.0%) were stroke of undetermined type. The 28-day case-fatality rate was 12% (95% CI 7% to 16%) for cerebral infarction, 45% (95% CI 30% to 60%) for intracerebral hemorrhage, 50% (95% CI 22% to 78%) for subarachnoid hemorrhage, and 38% (95% CI 18% to 57%) for stroke of undetermined type. Conclusions — The overall distribution of stroke subtypes and 28-day case-fatality rates are not significantly different from those of most European countries or the United States. There may, however, be some differences in the incidence of subtypes within Australia.