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| Journal of the New Zealand Medical Association,
17-November-2006, Vol 119 No 1245
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Incidence of stroke in women in Auckland, New Zealand. Ethnic
trends over two decades: 1981–2003
Lorna Dyall, Kristie Carter, Ruth Bonita, Craig Anderson,
Valery Feigin, Ngaire Kerse, Paul Brown; on behalf of the Auckland Regional
Community Stroke (ARCOS) Study Group
The lifetime risk of stroke in women (1 in 5) is greater
than in men (1 in 6).1 Stroke is the third
major cause of death in women in New Zealand after heart disease and cancer. Its
impact on women as one of the major causes of mortality, morbidity, and ongoing
disability is recognised but needs to be given more consideration with an
increasing aging and ethnically diverse New Zealand
population.2 In New Zealand, men have a higher
rate of stroke events. In contrast, New Zealand women experience more stroke
events in absolute terms and have poorer health outcomes following their stroke
in comparison to
men.2,3
On average, women in New Zealand have their first stroke
event 5 to 10 years later than men.3 With an
aging population it is expected that more women will experience stroke. Due to
their age, other health problems and personal circumstances are likely to need
assistance with daily life activities such as cooking and bathing, and some will
require ongoing nursing or institutional
care.2,4
As women often have their stroke later in relation to men
they are also usually the most important family caregivers. Their state of
health can affect the health and wellbeing of other family members and demands
placed upon them in providing care to men and others within their social network
can also increase their risk of
stroke.5
Over the last 20 years, a modest decline in the standardised
incidence rate of stroke in New Zealand has occurred, with gender and ethnic
differences emerging.3 The Auckland Community
Stroke Study suggests that Europeans have the highest crude incidence of stroke,
followed by Pacific (i.e. mostly of Samoan, Tongan, Niuean,
or Cook Islands
origin) and Māori then Asian plus Others.
However,
Māori and Pacific peoples have a greater age standardised incidence rate of
stroke and more unfavourable trend in stroke incidence over the last 20
years.1 Furthermore,
Māori and Pacific
people also have their stroke 10 to 15 years earlier in comparison to
Europeans.1 For subtypes of stroke,
Māori, Pacific,
and Asian have a higher age-adjusted risk of ischaemic stroke and primary
intracerebral haemorrhage compared with New Zealand
Europeans.6
This paper discusses the incidence of stroke as well as risk
factors and 28 day case fatality for women in Auckland, New Zealand from 1981 to
2003. Emerging ethnic differences are discussed to expose the picture of stroke
for women in New Zealand so as to assist future planning for the prevention of
stroke, the provision of treatment services, and to consider the rehabilitation
and support needs of women now and in the future.
Subjects and MethodologyThree population-based stroke
incidence studies were conducted in Auckland, New Zealand, covering the
following periods 1981–82, 1991–1992, and 2002–3, and have
been reported elsewhere.1,3 These studies have
been shown to meet the stringent criteria for ‘ideal’ stroke
incidence studies, such as involving a large representative population using
consistent methodology and definitions of
stroke.7–9
The first study was conducted between 1981–1982,
involved a sample 50% of Auckland’s primary care general practitioners
(GPs), identified using a cluster sampling approach, to produce a random sample
of half of all new stroke events in the
population.10 The second study was conducted in
1991–1992 and used a register of all cases of acute stroke managed in
hospital and a cluster sample of 25% of all GPs to estimate the number of
‘non-hospitalised, non-fatal’
events.11 The third study involved collecting
all new cases of stroke in
2002–2003.3
During the course of the three studies, the size of the
Auckland population has increased significantly and has become more ethnically
diverse thus making Auckland one of the largest growing urban centres in
Australasia. Auckland is a cosmopolitan city with a significant indigenous
Māori population
as well as growing Pacific and Asian populations due to increasing immigration.
Across
all study periods, ethnicity was defined by self-identification and grouped
according to NZ/European, Māori, Pacific peoples, and Asian plus Others as
in each national Census. Each study followed shortly after each Census.
The numerator and denominator for each ethnic group has been consistent, as
defined by Statistics New Zealand, thus allowing for appropriate ethnic
classification, for ethnic trends to be identified, and for miscalculation of
ethnicity to be minimised.1
All original data from the 1981–1982 and
1991–1992 studies were reviewed and re-analysed, and rates
re-calculated.3 The Cochrane-Armitage method
was used to test for the significance of trends in the distribution of
categorical variables and the Kruskal-Wallis non-parametric analysis of variance
was used for continuous variables.
Crude annual stroke incidence (first-ever events) and
attack (all events) rates per 100,000 people, together with 95% confidence
intervals (CI), were calculated using Poisson distribution, with adjustments
made for the sampling procedure in each of the first two ARCOS studies.
Standardised rates were calculated by the direct method of adjusting to the age
distribution of the WHO ‘world’
population.12
Standardised rate ratios (RR) were calculated to examine the change in rates
between the study periods.
ResultsDemographic
profile and characteristics of stroke in Auckland women—According
to the Census data 2002–, 66% of the population self identified as New
Zealand (NZ)/European (Pakeha), 9%
Māori, 11%
Pacific, and 14% Asian; other ethnic groups and women accounted for 53% of the
total Auckland population. Since 1981, the Auckland population has aged, with a
43% increase in people aged over 75 years, has undergone a doubling in the
proportion of
Pacific people, and a 10-fold increase in Asian and Other groups due to
immigration while the Māori population has not changed markedly in size.
The proportion of women experiencing stroke was stable
across the three studies (Table 1). Over the course of
the three studies, the mean age of onset of stroke in women increased overall
from 73.8 years in 1981–1982 to 74.3 years in 1991–92 and finally to
75.8 years in 2002–2003 (p=0.004). The average age at onset of stroke
increased across all ethnic groups except Asian and Other, although this latter
group was complicated by small numbers. On average,
Māori and Pacific
women had their strokes 15 years younger than NZ/European
women.
The ethnic profile of women experiencing stroke in Auckland
changed over the course of the three studies, with the proportion of New Zealand
European declining and the proportion of Pacific and Asian and Other populations
greatly increasing (due to increases in immigration in these populations).
Approximately one-third of the women were partnered at the
time of their stroke, thus suggesting two-thirds of women were unpartnered. In
comparison, two-thirds of men were partnered (thus one-third on their
own).
Over 50% of women who experienced a stroke event reported
that they had high blood pressure, and one in four had previously had a stroke.
These findings were stable across all three studies and also across ethnic
groups. The number of women reporting that they had diabetes increased
significantly from 8.6% in 1981–1982 to 15.4% in 2002–2003.
Smoking in women declined significantly: from 20% in
1981–1982 to 10% in 2002–2003 over the course of the three studies
in all ethnic groups.
Demographic and risk
factors—Table 2 shows demographic and risk
factor changes for women recorded for all three studies across ethnic groups.
Differences can be seen
but due to low number
of Māori, Pacific, and Asian plus Other women who have experienced stroke
during the course of each of the three studies; most variations are not
statistically significant.
High blood pressure for all ethnic groups of women, with the
exception of
Māori, has generally risen. A growing group of women have experienced a
stroke event previously, although for Māori there has been a decline in
2002–3. Myocardial infraction has risen for all groups of women with the
exception of Māori. The
number of women
reporting that they are a current smoker has declined although there is a
significant difference in the number of Māori women, where over a third
report that they smoke in comparison to Pacific 13%, Europeans 10%, and Asian
plus Other <4%.
Diabetes mellitus has been variable across the three studies
but there are ethnic differences beginning to emerge. With the exception of
Pacific women in 2002–3, all other ethnic groups of women have experienced
weight gain measured by BMI.
Incidence of
stroke—Age standardised incidence rates for women were relatively
stable across the three study periods with a rate ratio between the
1981–1982 and 2002–2003 studies of 0.93 (95%CI: 0.80–1.07) (Table 3). There was a significant decline in incidence
rates between 1991–1992 and 2002–2003 studies (RR 1991:2002 0.86;
95%CI: 0.76–0.98), due to an increase incidence between 1981–1982
and 1991–1992.
Incidence of stroke for women of different ethnic groups
varied in Auckland across the three studies (Table 3). NZ/European women
experienced a significant decrease in the incidence of stroke from
1981–1982 to 2002–2003 for both first ever and total events. The
rate in 1981–1982 for all stroke events for NZ/European women was 177 and
which fell to 148 by 2002–2003 leading to a significant decline of 16% (RR
1981:2002 0.84 [95%CI: 0.73–0.96]).
For
Māori women, the rate of first ever and total strokes increased from
1981–1982 to 2002–2003; this increase was not found to be
significant. There was almost a three-fold increase in total stroke event
rates for Pacific women across the study periods (RR 1981:2002 2.71; 95%CI
1.00–7.29). For Asian and Other women, the number of total stroke events
varied with an overall decline in event rates from 1981–1982 to
2002–2003 (RR 0.45, 95%CI 0.21–0.98); the wide CIs reflect the small
numbers for this population.
Case fatality after
stroke—There were significant declines in 28-day case fatality in
women, with a 39% relative decline, across the three studies (Table 4). These
declines were also seen across the ethnic groups; the numbers were too small in
the minority groups to reach levels of significant.
Table 4. 28-day case fatality in all female cases in
Auckland, New Zealand, 1981–2003
*There are 24 female cases
with missing ethnicity in the 2002–2003 study.
DiscussionOverall the three studies provide
convincing evidence that as women age and live longer, they are likely to have
an increased risk of experiencing a stroke event especially for those aged over
75 years of age. Even so, the incidence rate of stroke for European women has
declined over the 20-year period suggesting that interventions introduced to
improve New Zealanders’ health, such as promoting a smokefree society are
having an impact but not so dramatic for other populations.
Results from the Auckland studies are generalisable to New
Zealand women as a whole. The studies provide an accurate account of the
incidence of stroke within the defined populations and periods, by utilising
multiple and overlapping sources of information. Changes in the definition of
ethnicity over the course of the three studies have been managed by following
Statistics New Zealand guidelines for the collection and management of ethnic
data.
Individuals with a dual ethnic identity have been allocated
to defined population groups enabling the numerator and denominator to be
consistent for each study. Ethnic differences in women in 2002–3 provide
an indication of future trends of stroke for women from different ethnic groups
and supports previous studies which identify ethnic disparities for stroke
within a population.13–15
Careful monitoring also needs to be in place to ensure that
women receive appropriate care. Women have poorer outcomes than men for stroke,
have higher total mortality and are treated differently when presenting with
symptoms of stroke, such as not receiving appropriate investigations to
ascertain the type, severity, and causes of their
stroke.2,16–19 The situation in New
Zealand is unlikely to be different from that reported in other developed
countries, thus suggesting that more attention should be paid to acute stroke
care and management in women.
When European women have their stroke in New Zealand they
are likely to be in their mid 70s, to not have a partner, to have other health
problems, likely to receive Government Superannuation, and may have limited
social and economic resources to call upon to help them cope with their stroke
event.
With changing family and work patterns in New Zealand,
informal care may be unable to be provided by family members, who are usually
women and this may become less common as women need to work. In the future, it
is likely that there will be an increased demand for community care, such as
home help and nursing care, as women age and have fewer people within their
social network from whom to can call upon for help.
Support for informal caregivers through provision of
information on stroke and basic training in nursing care would enable them to
provide care for frail elderly female stroke
survivors.20
Over the course of the 20-year period, the incidence rate of
first-ever strokes for
Māori women
increased but the trend was not significant. Due to high prevalence of smoking
amongst Māori women in the general population, heart disease is often a
cause of death for Māori women and perhaps reduces the number to experience
a stroke event
later in their
lives. However, in the future, more Māori women may experience a stroke
event due to increasing rates of obesity and diabetes within the Māori
population.21–23
The first onset of stroke for
Māori women
occurs, on average, at 60 years and is approximately 15 years earlier than for
European or Asian and other women. This differential has significant
socioeconomic and health implications for Māori women and their families as
informal care often
requires one or more
family member giving up full or part time employment, resulting in loss of
income. This situation for the survivor and caregiver can increase existing
social, economic, and health disparities which exist between Māori and
non-Māori in New Zealand. This disparity requires appropriate
considerations by health and social care decision-makers.
The rate of total strokes for Pacific women has increased
almost three-fold over the 20-year period but the causes of this unfavourable
trend are not fully understood but may be related to population increase or some
differences in case attainment over the 20-year period, such as sampling
procedures used in the first two studies.
On average, Pacific people have their stroke close to 65
years of age and are eligible for Government Superannuation. For Pacific women
there has been an increase in stroke events for 2002–2003, with almost a
third having more than one stroke event in the year.
Overall, the Pacific population has a higher 28-day case
fatality rate than other ethnic groups thus suggesting that management of stroke
for Pacific people in New Zealand is an area which requires further
investigation before the impact of increasing prevalence of obesity and diabetes
becomes more profound in this population.
For Asian and other ethnic groups in New Zealand, their rate
of stroke between 1991–92 and 2002–3 has increased, though
statistically non-significant, and this reflects the changing ethnic and aging
demographic population in New Zealand. Although the proportion of Asian and
other populations in New Zealand is growing, this group currently has their
stroke at a similar age as the Pacific population. The pattern of stroke for
this population may change, however, as this population adopts lifestyles which
increase their risk of stroke, such as increased smoking and weight
gain.
Overall, the results from the three studies over two decades
show differences in stroke incidence between ethnic groups of women in New
Zealand. There are clear differences in the average age of stroke for women from
different ethnic groups and this places different demands and stresses on their
families and their ability to provide informal care.
The ability of family members in being able to provide
informal care in the future will depend upon many different factors, including
family members’ state of health, family circumstances, employment,
location where family members live, and general financial position. Some family
members may be unable to so female stroke survivors will then be dependent upon
community services and health institutions.
It has been predicted, utilising information from the
1991–1992 study, that if no major changes occurs in relation to stroke
prevention and management, New Zealand can expect to see a 10 to 50% increase in
the incidence and prevalence respectively of
stroke.22 However, if the incidence rate and
one year case fatality rates for stroke falls by 1% across all ethnic
populations the expected increase in stroke deaths would be reduced by
two-thirds.22
The incidence of stroke and the 1-month fatality rate has
fallen for European women over the period of observation. These changes are
positive however with aging, the rising rate of diabetes, and other factors the
effects of efforts towards reducing the burden of stroke will be
limited.
The observed pattern in stroke incidence in New Zealand
European women increased between 1981–82 and 1991–92 and decrease
incidence between 1991–92 and 2002–3 is unlikely to be affected by
methodological differences in case attainment between the
studies.3
In conclusion, the three studies conducted over a 20-year
period using similar methodology enable ethnic and gender trends to be analysed
in order to improve interventions aimed at modifiable risk factors of stroke. As
women make up the greatest proportion of caregivers, identifying support at an
early stage may help alleviate the stresses and demands placed on the community
and informal care givers who provide support to stroke survivors.
Conflict of interest
statement: The authors have no potential conflicts of interest.
Author information:
Lorna Dyall, Senior
Lecturer Māori
Health; Paul Brown, Senior Lecturer Health Services; Ngaire Kerse, Associate
Professor, General Practice; Ruth Bonita, Professor Emeritus; Valery
Feigin, Associate Professor, Clinical Trials Unit;
School of Population Health, Faculty of Medical and Health Sciences, University of Auckland, Auckland Kristie Carter, Research Fellow; Craig Anderson, Professor;
The George Institute for International Health, The University of Sydney and
Royal Prince Alfred Hospital, Sydney, Australia
Funding:
The Health Research Council of New Zealand funded the study but had no
input into the design, performance, analysis, or reporting of the study, and did
not see the manuscript prior to publication.
Acknowledgements: We
are indebted to the research nurses for their dedication and performance; the
support of staff at the Coroner’s Office in Auckland; the assistance of
staff of the New Zealand Health Information Service; the help provided by staff
at the Auckland office of the New Zealand Stroke Foundation; the support of many
doctors, nurses, and administrative staff within and outside Auckland; and of
course the ARCOS participants and their families and friends.
Correspondence: Dr
Lorna Dyall, Division of
Māori Health,
School of Population Health, University of Auckland, Private Bag 92019,
Auckland. Fax: (09) 303 5974; email: l.dyall@auckland.ac.nz
References:
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