The prevalence of stroke and associated disability - Oxford Academic

Journal of Public Health Medicine

Vol. 21, No. 2, pp. 166–171 Printed in Great Britain

The prevalence of stroke and associated disability Paul G. O’Mahony, Richard G. Thomson, Ruth Dobson, Helen Rodgers and Oliver F. W. James

Abstract Background There are limited data available on the prevalence of stroke in the United Kingdom. Such data are important for the assessment of the health needs of the population. This study aimed to determine the prevalence of stroke and the prevalence of associated dependence in a district of northern England. Methods This was a two-stage point prevalence study. A valid screening questionnaire was used to identify stroke survivors from an age- and sex-stratified sample of the population aged 45 years and over in a family health services authority district. This was followed by assessment of stroke patients with scales of disability and handicap. Results The overall prevalence of stroke was found to be 17.5/1000 (95 per cent confidence interval (CI) 17.0, 18.0). The prevalence of stroke-associated dependence was 11.7/1000 (95 per cent CI 11.3, 12.1). Self-reported comorbidity was most commonly due to circulatory and musculoskeletal disorders. Conclusions The prevalence of stroke in this district is considerably higher than current guidelines and previous results suggest. Nevertheless, the result from this study combined with that from a previous study in another district in the United Kingdom should allow those interested in epidemiologically based health needs assessment to make reasonable estimates of the burden of stroke in their area. Keywords: stroke, prevalence, disability, health needs assessment

Introduction Although mortality rates from cerebrovascular disease appear to be declining in most industrialized nations (by up to 5 per cent per year), stroke remains the third most common cause of death in the United Kingdom (UK).1 Moreover, stroke disease is a major cause of morbidity and long-term disability and handicap.2 The Oxfordshire Community Stroke Project provided valuable data on stroke incidence and outcome.3 However, such data are insufficient for describing the true impact of stroke and identifying the continuing health and social needs of these patients. Of more relevance to the care of long-term stroke survivors is the prevalence of the condition and the prevalence of associated disability and handicap.

Until recently, there have been limited data available on stroke prevalence in the UK. Many previous prevalence estimates have been calculated either from incidence and survival data, or from disability surveys.4–6 An epidemiologically based health needs assessment advised the use of an average figure of 600 per 100 000 for stroke prevalence, basing this on studies from the United States, Scandinavia and elsewhere.7 However, it is difficult to confidently extrapolate results from other countries to a British population, given the fact that incidence rates and mortality vary considerably between countries.8 Furthermore, the wide geographical variations in mortality in the UK may be reflected in similar variations in prevalence.9 Although a 1971 survey by Harris suggested that stroke accounts for 24 per cent of severe disability in the community, the true level of disability associated with stroke in our population is unclear.10 Knowledge of the prevalence of disability and handicap associated with stroke is essential for determining the impact of stroke on health and social service providers and for planning for adequate service provision. The first definitive study of stroke prevalence in this country has recently been published, reporting a lifetime prevalence of 1470 per 100 000 for stroke in a district in Yorkshire,11 a result which is clearly greater than has been suggested previously.7 The same study found a point prevalence of stroke-associated disability of 620 per 100 000, also higher than the figure suggested as a guidance for health care purchasers. For accurate health and social service planning, we cannot necessarily apply the Yorkshire results to any other districts or regions without good evidence of similar stroke epidemiology. The former Northern Region had the highest standardized mortality ratio from stroke of any English health region.9 We Departments of Medicine (Geriatrics)1 and Epidemiology and Public Health2, University of Newcastle, Newcastle upon Tyne NE2 4HH. Paul G. O’Mahony, Research Registrar1,2 Richard G. Thomson, Senior Lecturer in Public Health Medicine2 Ruth Dobson, Research Associate1,2 Helen Rodgers, Senior Lecturer in Stroke Medicine and Services1,2 Oliver F. W. James, Professor of Medicine (Geriatrics)1 Address correspondence to Richard Thomson.

䉷 Faculty of Public Health Medicine 1999

PR EVAL ENCE OF STROKE

determined the prevalence of stroke and associated disability in a district of this region.

Methods A random age- and sex-stratified sample of 2000 persons aged 45 years or over was selected from the former Newcastle Family Health Services Authority (FHSA) register. Two hundred persons were chosen in each ten year age–sex group (45–54, 55–64, 65–74, 75–84, and 85+ years). At the time of the study, the district was estimated to have a total population of 285 310, of whom 100 954 were aged 45 years or over.12 Methods have been described in detail elsewhere.13 A brief screening questionnaire was posted to all subjects with a letter co-signed by general practitioners (GPs) and a freepost envelope for its return. The questionnaire included the question ‘Have you ever had a stroke?’ and two questions aimed at determining dependence status.14 The prevalence date was taken as the date of posting. The Newcastle Joint Ethical Committee approved the study. Validation of the screening question involved a standardized home assessment visit for those reporting a history of stroke, and accessing multiple sources of case ascertainment for all 2000 subjects. Letters requesting the home visit were followed by two reminders where necessary. In cases where the most recent stroke was less than six months previously, the visit was planned for a minimum of six months after the patient’s (most recent) stroke at a time when near maximum recovery would have been expected. General practice records, hospital case notes, a local stroke register and the Regional Informations Systems database were accessed as sources of case ascertainment. This validation process for the screening questionnaire, therefore, allowed identification of definite cases of stroke among negative and non-responders.13 All such patients were also offered the home assessment interview after approval had been sought from their GP. The home visit incorporated a detailed history and examination to allow the examiner (P.O’M.) to confirm or refute the diagnosis of stroke. Stroke was defined according to World Health Organization criteria, i.e. ‘Rapidly developing clinical signs of focal or global disturbance of cerebral function with symptoms lasting 24 hours or longer . . . with no apparent cause other than of vascular origin’.15 The interview inquired about basic demographic data, about the patient’s stroke(s), and self-reported comorbidity. The comprehensive structured interview also included scales of disability (Barthel Activities of Daily Living (ADL) Index16) and handicap (Oxford Handicap Scale17). Assessments of mental function and communication skills were incorporated to determine suitability for interview. If the patient scored less than 7/10 on the Abbreviated Mental Test Score (AMTS),18 or had evidence of severe communication difficulty, information was collected by proxy from the patient’s primary carer. The home visit assessment was

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pretested with stroke patients living in an area outside the study district. The prevalence of stroke was calculated for the population sample chosen, and corrected to the total district population. To obtain a more precise estimate of stroke prevalence in the district, the cases of stroke resident in long-term National Health Service (NHS) nursing care units were also ascertained. Cases were identified by asking the physician and/or senior nurse in charge of the wards of such units to indicate which of their patients had a history of stroke. At the time of the study, there were an additional 53 cases of stroke in such care. Such patients are not registered with GPs and, therefore, are not included on the FHSA register. Data were entered onto a specifically designed relational database, and statistical analysis was performed using t-tests for comparison of means and x2 tests for comparison of proportions.

Results The screening questionnaire had a response rate of 88 per cent (1663/1880) when corrected for those who had died, were not at their registered address or had been excluded.13 There were 173 respondents who answered positively to a history of stroke. Of these, 104 were subsequently determined to have definitely had a stroke by the validation procedure and 71 (68 per cent) of them agreed to a home assessment visit. Six cases of stroke were identified among negative responders (n ¼ 1490) to the screening question, of whom two agreed to be visited. A further six cases were ascertained from non-responders (n ¼ 217), three of whom were visited. The proportion of stroke patients identified among responders (110/1663) was significantly greater than the proportion among non-responders (6/217), (P < 0:005). For the 110 confirmed cases of stroke who responded to the screening questionnaire, 62 (56 per cent) reported requiring help from another person to perform everyday activities, and 64/98 (65 per cent) felt they had not made a complete recovery from their stroke. There were no significant differences in the responses to these two questions on the screening questionnaire between those who had a home assessment visit and those who did not (P > 0:05 for both questions).

Prevalence of stroke The age- and sex-specific and age- and sex-adjusted prevalence rates for stroke are shown in Table 1, with comparative rates from the Yorkshire study.11 A similar trend across age groups is seen between the two British studies, with the prevalence being higher among males than among females for all age groups except for those aged 85 years and over. For age groups above 65 years, the results from the two studies are similar, with closely overlapping confidence intervals. For the younger age groups, there is less close agreement because our study had

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Table 1 Age- and sex-specific and age- and sex-adjusted lifetime prevalence rates for stroke and for stroke-associated dependence in Newcastle upon Tyne, with comparative figures for stroke prevalence for North Yorkshire11

Prevalence rate /1000 (95% CI)

Comparative prevalence rates from Yorkshire11

No. of stroke survivors assessed for dependence

No. of dependent stroke survivors/ no. of stroke survivors assessed

1 6 10 15 21

5.1 (0.0, 14.9) 30.8 (6.5, 55.0) 51.3 (20.3, 82.2) 77.3 (39.7, 114.9) 112.3 (67.0, 157.6)

n.a. 11.4 (6.9, 17.8) 33.9 (25.6, 44.0) 79.7 (64.8, 97.3) 104.4 (77.0, 137.3)

1 5 7 13 11

0/1 3/5 6/7 10/13 10/11

0.0 (0.0, 0.0) 18.5 (0.0, 37.4) 44.0 (15.2, 72.7) 59.5 (26.2, 92.8) 102.1 (58.7, 145.5)

2 9 13 27 12

11.0 (0.0, 26.1) 47.6 (17.3, 78.0) 69.9 (33.3, 106.5) 143.6 (93.5, 193.7) 71.4 (32.5, 110.4)

n.a. 21.6 (15.0, 31.2) 46.8 (36.0, 59.7) 110.1 (87.5, 136.5) 82.2 (43.7, 146.5)

1 6 11 14 7

1/1 3/6 5/11 11/14 6/7

11.0 (0.0, 26.1) 23.8 (2.1, 45.5) 31.8 (6.6, 57.0) 112.8 (67.6, 158.1) 61.2 (25.0, 97.5)

3 15 23 42 33

7.9 (0.0, 16.8) 39.1 (19.7, 58.4) 60.4 (36.5, 84.3) 109.9 (78.6, 141.3) 93.0 (62.8, 123.2)

n.a. 16.4 (12.3, 21.5) 39.8 (33.3, 47.7) 91.1 (78.5, 105.7) 98.4 (75.5, 126.0)

2 11 18 27 18

1/2 6/11 11/18 21/27 16/18

3.9 (0.0, 10.3) 21.3 (6.9, 35.8) 36.9 (18.0, 55.8) 85.5 (57.4, 113.5) 82.7 (54.0, 111.3)

Age or sex group

Effective population sample

Number of stroke cases

Females 45–54 55–64 65–74 75–84 85þ

198 195 195 194 187

Males 45–54 55–64 65–74 75–84 85þ

182 189 186 188 168

Females and males 45–54 380 55–64 384 65–74 381 75–84 382 85þ 355

All 45þ (age- and sex-adjusted)

47.4 (46.1, 48.7)

All ages (age- and sex-adjusted)

17.5 (17.0, 18.0)

Prevalence rate of dependent stroke survivors*

32.9 (31.8, 34.0) 14.7

11.8 (11.4, 12.2)

n.a., not available. * Dependence determined by a score of < 20 on the Barthel ADL Index or 3–5 on the Oxford Handicap Scale.

proportionately less younger subjects with stroke, and the broad confidence intervals reflect this.

Demography The mean age of the 76 stroke patients assessed at the home visit (77.3 (SD 10.1) years) was not significantly different from that of the 40 subjects not visited (80.5 (SD 10.1) years), P > 0:1. The age range of patients visited was 52–96 years; there were 39 (51 per cent) males and 37 (49 per cent) females. Thirty-four (45 per cent) were married, 33 (43 per cent) widowed, 6 (8 per cent) single or never married and 3 (4 per cent) separated or divorced.

Comorbidity Of the 76, 46 (61 per cent) had suffered one stroke only, 25 (33 per cent) more than one, and reliable information was not available for the remaining five (6 per cent). The frequency of self-reported (or proxy-reported) comorbidity is shown in Table 2. A total of 14 (18 per cent) subjects obtained a score of less than 7/10 on the Hodkinson AMTS.

Disability and handicap Using the Oxford Handicap Scale, 23 (30 per cent) scored 0–2, indicating independence, whereas 53 (70 per cent) scored 3–5, suggesting dependence. Using the Barthel ADL Index, a very similar proportion (29 per cent) were fully independent, attaining the maximum score of 20 on the scale. For determining the prevalence of dependent stroke survivors Table 2 Prevalence of self-reported (or proxy-reported) comorbidity among the 76 stroke patients who received a home assessment visit (numbers, with percentages given in parentheses) Comorbid condition

Patients

High blood pressure Arthritis or rheumatism Circulation trouble Heart trouble Diabetes Others*

33 (43) 32 (42) 28 (37) 27 (36) 10 (13) 47 (62)

*Other health problems reported included epilepsy, emphysema and chronic bronchitis, asthma, Parkinson’s disease, thyroid disorders and skin disorders.


among subjects aged 45 years and over, the worst result of the two scales was chosen for each individual stroke patient (Table 1). To allow calculation of the all-ages prevalence in the population, it was assumed that the maximum proportion of stroke subjects aged less than 45 years who are disabled is 25 per cent.19

Discussion Knowledge of the true prevalence of stroke both locally and nationally is necessary for determining the impact on patients and carers, social services and health care providers and purchasers. Of greater importance for such groups are reliable data on the prevalence of stroke-associated disability and handicap to allow assessment of the consequent health needs. Our study provides valuable results for these variables.

Bias of population sample Our sampling method had proportionately greater numbers of older subjects. This was to ensure accurate determination of both the validity of our screening questionnaire and stroke prevalence among the age groups in which it is most common. The reporting of our demographic data, therefore, is biased towards older stroke survivors and does not reflect the actual population structure. Nevertheless, we present age- and sexspecific prevalence rates for stroke and for associated dependence, and age- and sex-adjusted rates. We have reported levels of disability and handicap of stroke survivors. Not all the disability and handicap in such subjects will specifically be due to the stroke. In fact, with increasing age, pre-stroke disability and handicap becomes more prevalent so that post-stroke dependence will inevitably have more causes. However, the data we present are of value, as purchasers of health care are interested in planning for services specifically for stroke patients, and the new White Paper on the future of the NHS strongly promotes programme-based commissioning centred around diseases.20 Some bias may have resulted from the collection of data by proxy. The data collected on demographic details are likely to be as accurate when collected from a proxy. It could be argued that the data concerned with impairment, disability and handicap may not be accurate if collected by proxy but there was no other feasible way of collecting the information from the most severely disabled subjects. In fact, carer assessment by Barthel ADL Index has been recommended for patients with cognitive deficits.21

Validity of diagnosis of stroke Although there may be a number of potential biases in our study, the screening questionnaire we developed for identifying stroke survivors produced a very high response rate, and has been validated.13 Other studies have not published such detail on the validity of their screening methods. The Danish and

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Finnish prevalence studies failed to follow up false negatives to their screening process and must therefore have underestimated the true prevalence of stroke.22,23 In the Yorkshire study, there is no mention of the specificity of the screening method used.11 Furthermore, the absence of any false negatives was stated after assessing the screening question on a relatively small number (n ¼ 150) of subjects of different (albeit overlapping) age range to the final study population. Although validated against a diagnostic index, only a small number of elderly subjects could have been included. As the older age groups are more likely to have cognitive problems and hence poorer memory of possible strokes, it is important to ensure adequate testing of validity in this group.

Prevalence of stroke Until recently we had very limited data on the prevalence of stroke in the UK. Our study now means there are two reports with definitive results of the prevalence of stroke and associated dependence. Our study aimed to determine the prevalence of stroke in the population aged 45 years or over. The Oxfordshire Community Stroke Project found that an additional 4 per cent of strokes occurred in the under 45 years age group.3 The prevalence for the total population in our study area could therefore be estimated as 1750/100 000 (95 per cent confidence intervals (CI) 1700, 1800). The additional 53 cases of stroke in long-term NHS nursing care can be added to the expected number of cases of stroke in the study population, giving a total prevalence of stroke of approximately 1770/100 000 (95 per cent CI 1720, 1820). A comparison of this rate with that from the recent study from Yorkshire (1470 per 100 000) confirms regional differences within the UK consistent with the known variations in mortality experience.11 Nevertheless, it is encouraging that both northern studies have found broadly similar results, suggesting that the previously quoted figure of 600/100 000 would be a substantial underestimate if applied to our population.7 It would seem likely that the Yorkshire study may have further underestimated the prevalence of stroke as a result of the assumption of no false negative responses in their final study population. Nevertheless, regional differences in incidence and survival are also likely to contribute to the variation.9,12,24 The two studies confirm that using prevalence rates from other countries as a basis for health needs assessment is inadvisable. There are an increasing number of stroke prevalence studies from other countries. As with studies of incidence, epidemiological studies of stroke prevalence are prone to specific biases. Therefore, it may be difficult to compare stroke prevalence rates from many of the studies available because of differences in, among other factors, the age and sex distribution of the population, the geographical diversity of the populations studied and the different methods used to determine prevalence. Although some researchers have standardized their prevalence results either to the population of the country being

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studied or to a standard European, US or world population, this is not consistent across all studies, nor is there consistency in the standard reference population used. Within Europe, the earliest prevalence studies were carried out in Scandinavia.22,23 More recent studies have been carried out in Italy,25 France26 and Norway.27 The result from the French study is the highest reported rate in Europe (outside the UK) and may reflect the fact that the region studied had, at the time, the oldest population of all regions of France or Europe. Age-specific rates were not given, thereby making a true comparison with other studies difficult. It is clear that there are wide international variations in stroke prevalence, in addition to national differences. The Norwegian study used a method which was well validated among elderly age groups, and found a prevalence of stroke of 1670/100 000, very similar to our result.27 Mortality rates are lower in Norway than in England and Wales, but have been declining at a similar rate.8 When standardized to the World Health Organization world standard population, the prevalence rate for stroke in those aged 55 years and over in our study is 35.0/1000. This compares with similarly standardized rates for Yorkshire, 25.8/10007 and New Zealand, 31.2/1000.28 For the Norwegian study, it is possible to standardize for those aged 50 years and over, giving a rate of 27.6/1000.27

Disability and handicap Using the two previously validated dependence questions, 56 per cent of our stroke patients reported requiring help from another person to perform everyday activities (compared with 55 per cent in the Yorkshire study), and 65 per cent felt they had not made a complete recovery from their stroke (compared with 80 per cent).11,14 The Yorkshire group calculated the prevalence of stroke-associated disability as 620 per 100 000 of the population.11 We estimated this figure to be approximately 1170/100 000 (Table 1), a result greater than previous estimates and more than twice that calculated in an earlier study.7 Including the cases of stroke in long-term NHS care (n ¼ 53) and assuming that all of those were dependent, the prevalence of dependent stroke survivors in the study population can be calculated as approximately 1200/100 000. The higher result from our study may have occurred because of a different method of determining dependence. We used the results from the Barthel ADL Index or Oxford Handicap Scale, whereas the Yorkshire group used self-reported disability for a number of everyday activities. The striking difference may also reflect the possibility of strokes being more severe in our district than in Yorkshire, or there may be some form of survival bias. Alternatively, rehabilitation services may be better in Yorkshire, leading to better outcome from stroke. This study’s results, alongside those of the study from Yorkshire, confirm that the age- and sex-specific prevalence of stroke in this country is considerably greater than previous estimates have suggested. Standardized rates, however, show

that there are similar rates in different countries. Of greater importance, this study emphasizes that the prevalence of strokeassociated disability is higher than realized. We feel that our data provide a useful basis for purchasing health and social care for stroke survivors in our district. Purchasers from other districts interested in adequately assessing the health needs of their population must be aware of these discrepancies, but could use the available data to provide a reasonable estimate of the prevalence of stroke within their area. The projected changes in the demography of the population make it important to assess the needs of, and plan services for, elderly people, as the numbers of elderly people at risk of stroke and associated dependence will continue to rise. Following the implementation of the NHS reforms in the early 1990s, purchasing authorities are required to set contracts for services which are based on an assessment of population need for health care. The latest NHS reforms stress the importance of health needs assessment by placing the emphasis on commissioning using disease-based programmes of care, further highlighting the importance of understanding local epidemiology. If done well, needs assessment could help to identify gaps in local health care provision or areas where existing services need to be redesigned or improved. However, to do it well requires accurate and up-to-date epidemiological data such as that provided by this study. This is not to imply that every district should undertake a similar study to ours, but that in applying such estimates from elsewhere it is certainly worth considering how applicable any such published data may be to the local area.

Acknowledgements We wish to acknowledge the financial support of the former Northern Regional Health Authority Research and Development Directorate.

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