Elsevier

The Lancet

Volume 363, Issue 9425, 12 June 2004, Pages 1925-1933
The Lancet

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Change in stroke incidence, mortality, case-fatality, severity, and risk factors in Oxfordshire, UK from 1981 to 2004 (Oxford Vascular Study)

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Summary

Background

The incidence of stroke is predicted to rise because of the rapidly ageing population. However, over the past two decades, findings of randomised trials have identified several interventions that are effective in prevention of stroke. Reliable data on time-trends in stroke incidence, major risk factors, and use of preventive treatments in an ageing population are required to ascertain whether implementation of preventive strategies can offset the predicted rise in stroke incidence. We aimed to obtain these data.

Methods

We ascertained changes in incidence of transient ischaemic attack and stroke, risk factors, and premorbid use of preventive treatments from 1981–84 (Oxford Community Stroke Project; OCSP) to 2002–04 (Oxford Vascular Study; OXVASC).

Findings

Of 476 patients with transient ischaemic attacks or strokes in OXVASC, 262 strokes and 93 transient ischaemic attacks were incident events. Despite more complete case-ascertainment than in OCSP, age-adjusted and sex-adjusted incidence of first-ever stroke fell by 29% (relative incidence 0·71, 95% CI 0·61–0·83, p=0·0002). Incidence declined by more than 50% for primary intracerebral haemorrhage (0·47, 0·27–0·83, p=0·01) but was unchanged for subarachnoid haemorrhage (0·83, 0·44–1·57, p=0·57). Thus, although 28% more incident strokes (366 vs 286) were expected in OXVASC due to demographic change alone (33% increase in those aged 75 or older), the observed number fell (262 vs 286). Major reductions were recorded in mortality rates for incident stroke (0.63, 0.44–0.90, p=0.02) and in incidence of disabling or fatal stroke (0·60, 0·50–0·73, p<0·0001), but no change was seen in case-fatality due to incident stroke (17·2% vs 17·8%; age and sex adjusted relative risk 0·85, 95% CI 0·57-1·28, p=0·45). Comparison of premorbid risk factors revealed substantial reductions in the proportion of smokers, mean total cholesterol, and mean systolic and diastolic blood pressures and major increases in premorbid treatment with antiplatelet, lipid-lowering, and blood pressure lowering drugs (all p<0.0001).

Interpretation

The age-specific incidence of major stroke in Oxfordshire has fallen by 40% over the past 20 years in association with increased use of preventive treatments and major reductions in premorbid risk factors.

Introduction

Stroke is the second leading cause of death worldwide1 and the main cause of long-term neurological disability in adults, with more than half of survivors being left dependent on others for everyday activities.2 It is also a major cause of depression, dementia, epilepsy, and falls, and patients with stroke account for more hospital and care-home bed days than any other disorder.2 The burden of stroke is predicted to increase over the years ahead because of the rapid rise in the elderly population in both the developed and developing world. However, over the past two decades, findings of randomised trials have shown that several interventions are effective in both the primary and secondary prevention of stroke,3, 4, 5, 6 and researchers have estimated that full implementation of currently available preventive strategies could reduce stroke incidence by as much as 50–80%.7, 8 Country-specific data on time-trends in stroke incidence are required to assess whether implementation of these preventive strategies has been associated with any such change.

Stroke mortality rates fell from the 1950s to 1980s in North America and western Europe,9, 10 but this decline has since levelled off.11, 12, 13 Although apparent trends in stroke mortality are very difficult to interpret because of changes over time in death certification practices and case-fatality, stroke incidence also seemed to diminish in the 1960s and 1970s in the USA,14, 15 Asia,16 and Europe.17, 18, 19 However, findings of most subsequent studies during the 1980s and 1990s, when effective preventive treatments had become more widely available, have shown either no change20, 21, 22, 23, 24 or an increase in age-adjusted and sex-adjusted incidence.25, 26, 27, 28, 29, 30, 31 Thus, as yet, no evidence is available that preventive strategies have reduced the incidence of stroke on a community level.

A population-based incidence study of stroke and transient ischaemic attack (the Oxfordshire Community Stroke Project; OCSP)32, 33 was undertaken in Oxfordshire, UK, 20 years ago. Because little change has taken place in either the racial mix of the population or in the organisation of the health-care system in the interim we had the opportunity to ascertain reliably the change in the incidence of stroke and transient ischaemic attack over the past 20 years. In collaboration with the original OCSP investigators, and using the same methods, we aimed to remeasure the incidence of stroke and transient ischaemic attack in the same population in 2002–04 (Oxford Vascular Study) and to compare premorbid use of preventive treatments and risk factors.

Section snippets

Study population

The OXVASC study population comprised all individuals, irrespective of age, registered with 63 family doctors in nine general practices in Oxfordshire, UK. In the UK, most people register with a general practice, which provides their primary health care and holds a lifelong record of all consultations with the family doctor and secondary-care providers and details of medications, blood pressure, and investigations. OXVASC included all practices that had participated in OCSP apart from two

Procedures

Diagnosis was designed to be as similar as possible to the OCSP. We used the same definitions of stroke and transient ischaemic attack.36 Furthermore, since clinical opinion about which clinical syndromes represent transient ischaemic attack or stroke has evolved over the past 20 years, summaries of all potential cases were reviewed by the principal investigator of OCSP (CPW) to ensure that the application of definitions of events was comparable. Diagnosis was based on clinical findings and CT

Results

476 individuals had at least one transient ischaemic attack or stroke during the study period. Of these, 262 were first-ever incident strokes (223 ischaemic strokes, 17 primary intracerebral haemorrhages, 16 subarachnoid haemorrhages, and six unknown) and 76 were recurrent strokes. 138 people presented to medical attention with at least one OCSP-compatible transient ischaemic attack during the study. Of these, 20 had a previous transient ischaemic attack, 17 had a previous stroke, and eight had

Discussion

We have shown a major reduction in the age and sex specific incidence of stroke in Oxfordshire, UK, over the past 20 years. As a result, the absolute number of strokes has fallen despite a 33% rise in the population older than 75 years of age and improved ascertainment of stroke in elderly people. This decline was associated with increased use of preventive treatment and better control of vascular risk factors.

Hospital-based studies are prone to bias because changes in patterns of referral,

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