Ascertaining the true incidence of stroke: experience from the Perth Community Stroke Study, 1989–1990

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Abstract
To determine the age and sex specific incidence, and case fatality of stroke in Perth, Western Australia. A population-based descriptive epidemiological study. All residents of a geographically defined segment of the Perth metropolitan area (population 138,708) who had a stroke or transient ischaemic attack between 20 February 1989 and 19 August 1990, inclusive. Definite acute "first-ever-in-a-lifetime" (first-ever) and recurrent stroke classified according to standard definitions and criteria. During the 18-month study period, 536 stroke events occurred among 492 patients, 69% of which were first-ever strokes. The crude annual event rate for all strokes was 258 (95% confidence interval 231-285) per 100,000, and the overall case fatality at 28 days was 24% (95% CI, 20%-28%). The crude annual incidence for first-ever strokes was 178 (95% CI, 156-200) per 100,000; 189 (95% CI, 157-221) per 100,000 in males and 166 (95% CI, 136-196) per 100,000 in females. The corresponding rates, age-adjusted to the "world" population, were 132 (95% CI, 109-155) for males and 77 (95% CI, 60-94) for females. In contrast to mortality rates for ischaemic heart disease, the incidence of stroke in Australia appears little different from that for several other Western countries. For both males and females the incidence of stroke rises exponentially with increasing age. Although the sex-dependent difference in the risk of stroke is greatest in middle age, males are at greater risk of stroke even among the most elderly. To determine the incidence of stroke accurately, population-based studies of stroke need exhaustive and overlapping sources of case ascertainment. If only cases admitted to hospital had been used, we would have underestimated the rate of stroke among the most elderly by almost 40%. We estimate that approximately 37,000 people, about 50% of whom are over the age of 75, suffer a stroke each year in Australia.