Incidence of the major stroke subtypes - Initial findings from the North East Melbourne Stroke Incidence Study (NEMESIS)

Background and Purpose-Population-based stroke incidence studies are the on ly accurate way to determine the number of strokes that occur in a given so ciety. Because the major stroke subtypes have different patterns of inciden ce and outcome, information on the natural history of stroke subtypes is es sential. The purpose of the present study was to determine the incidence an d case-fatality rate of the major stroke subtypes in a geographically defin ed region of Melbourne. Australia. Methods-All suspected strokes that occurred among 133 816 residents of subu rbs north and east of Melbourne, Australia, during a 12-month period of 199 6 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% Cl 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% Cl 5.4% to 12.0%) were stroke of undetermined type. The 28-day case-fatality rate was 12% (95% Cl 7% to 16%) for cerebral infarction. 45% (95% Cl 30% to 60%) for intracerebral hem orrhage, 50% (95% Cl 22% to 78%) for subarachnoid hemorrhage, and 38% (95% Cl 18% to 57%) for stroke of undetermined type. Conclusions-The overall distribution of stroke subtypes and 28-day case-fat ality rates are not significantly different from those of most European cou ntries or the United States. There may, however, be some differences in the incidence of subtypes within Australia.