Published online before print February 3, 2005, doi: 10.1161/01.STR.0000155687.18818.13
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(Stroke. 2005;36:551.)
© 2005 American Heart Association, Inc.
Original Contributions |
Prevalence of Stroke Among Chinese, Malay, and Indian Singaporeans
A Community-Based Tri-Racial Cross-Sectional Survey
From the Departments of Neurology (N.V., L.C.S.T., E.S.K.), National Neuroscience Institute; Geriatric Medicine (S.S., J.J.C.), Tan Tock Seng Hospital; and Community, Occupational and Family Medicine (C.Y.H., S.M.S.), National University of Singapore.
Correspondence to Dr N. Venketasubramanian, Department of Neurology, National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore. Email ramani_nv{at}ttsh.com.sg
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Abstract |
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Background and Purpose— Stroke prevalence data among mixed Asian populations are lacking. Prevalence rates of stroke were studied among Singaporeans aged
50 years of Chinese, Malay, and Indian origin. Methods— Study participants were selected by disproportionate stratified random sampling by race. Trained interviewers performed face-to-face interviews with subjects using the World Health Organization screening protocol for neurological diseases. Data were also collected on a self-report of stroke. Subjects suspected to have had a stroke underwent a clinical evaluation to diagnose or exclude stroke. Case notes review was performed for those who were unable to come for clinical evaluation.
Results— The study involved 14 906 participants: 6734 men, 8172 women, age range 52 to 106 years, Chinese:Malay:Indian ratio 3:1:1. Participation rate was 66.9%. Six hundred and six were diagnosed to have a stroke, yielding a crude prevalence rate of 4.05% (95% CI, 3.75 to 4.38) and a World Health Organization world population age-gender-standardized rate of 3.65% (95% CI, 3.36 to 3.96). Prevalence rates rose with age (P<0.001 for trend) and were higher among men compared with women, 4.53% (95% CI, 4.05 to 5.07) versus 2.91% (95% CI, 2.57 to 3.29), P<0.01. Age and gender-standardized rates among Chinese, Malays, and Indians were 3.76% (95% CI, 3.38 to 4.17), 3.32 (95% CI, 2.72 to 4.07), and 3.62% (95% CI, 2.95 to 4.44), respectively, P>0.2. Prevalence was highest among Chinese men at 4.78% (95% CI, 4.14 to 5.50) and lowest among Malay women at 2.81% (95% CI, 2.08 to 3.81), P=0.01.
Conclusions— There is no difference in stroke prevalence among Chinese, Malay, and Indian Singaporeans. Prevalence is highest among Chinese men and lowest among Malay women. The reasons for these differences warrant further investigation.
Key Words: cerebrovascular disorders • developing countries • epidemiology
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Introduction |
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Stroke is a leading cause of death and disability.1 A review of 9 recently published community-based studies reported an age and sex-standardized stroke prevalence of 4.6% to 7.3% among populations aged
65 years.2 Many estimates of stroke prevalence are based on white people in developed countries.3–8 Large studies among Asian populations are scant outside of Japan, China, Taiwan, and India.9–18 The few inter-racial comparative studies were performed among black and white Americans.19–21 More needs to be known about stroke prevalence among the ethnically diverse populations of Asia.
Singapore is a tropical island city-state of 4 million, comprising 77% Chinese, 14% Malays, and 8% Indians, with ethnic origins in southern China, India, and Malaysia. Among the 681 282 aged 50 years, the ethnic distribution is 81%, 10%, and 7%, respectively. Health care is easily accessible and heavily subsidized by the government. Stroke is the fourth leading cause of death in Singapore.22 The main aim of the Stroke, Parkinson’s Disease, Epilepsy and Dementia in Singapore (SPEEDS) study is to determine the prevalence of major neurological diseases among Singapore adults aged 50 years. The secondary aim is to investigate inter-racial and gender differences in the prevalence of these diseases. This article reports the prevalence of stroke.
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Subjects and Methods |
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Study Area
The study was conducted between April 2001 and June 2003 in Ang Mo Kio, Bishan, Serangoon, Toa Payoh, and Yishun districts in central Singapore. The demographic profile of this area resembles the rest of the country.23
Inclusion Criteria
Men and women were eligible for the study if they were Singapore citizens or permanent residents of Chinese, Malay, or Indian origin, aged 50 years, and resident in the study area on reference day 2 April 2001. Residents of institutions were eligible if on reference day they resided in a nursing home within the study area. Stroke status was assessed as of their date of interview.
Participant Selection
The Ministry of Home Affairs keeps regularly updated records of all residents in Singapore. The sampling frame comprised all Chinese, Malay, and Indian Singaporeans aged 50 years living in the study area. Simple random sampling was performed, disproportionately stratified by race in a Chinese:Malay:Indian ratio of 3:1:1 to allow the 3 main races to be adequately represented.
Phases of the Study
In Phase 1, an invitation letter was sent followed by a phone call to make a study appointment. A 15-minute face-to-face interview was performed by trained interviewers in the participant’s home. A standardized questionnaire was used to record information on demographics and screen for neurological diseases. The World Health Organization (WHO) Protocol for Neurological Diseases was used as the screening tool for stroke.24 Questions on headache were removed as they were not relevant to the study aims. Participants were also asked if they had ever been told by a doctor to have had a stroke. Repeated attempts were made to contact potential subjects, including telephone calls and 3 weekend and nighttime home visits.
Participants identified to potentially have neurological disease or who self-reported a stroke underwent a Phase II clinical review in their homes or at a community center nearby. This was performed by neurologists and geriatricians; interobserver variability testing yielded a 
of 0.93. Participants were identified as stroke patients if they met the WHO definition for stroke.25
Phase III comprised medical records review for Phase II–eligible participants who could not be reviewed because of death or who could not be contacted for Phase II review despite 3 good attempts including 3 home visits. Records were obtained from the polyclinics and hospital in the study area and reviewed for documentation of a stroke.
Quality Assurance
All interviewers underwent a day-long training program comprising detailed review of the questionnaire, demonstration of interview technique, and back-demonstration by the interviewer. The study questionnaire was forward- and back-translated into Chinese, Malay, and Tamil and reviewed by bilingual individuals for accuracy. A telephone call by the study coordinator to a randomly selected 10% of study participants confirmed that they had indeed been interviewed. Completed Phase I data forms were scanned in by an optical scanner; data entry accuracy was ensured by a manual check of all forms. Phase II and III data were entered manually, and entered data independently checked by another person.
Sample Size Estimation
Using Epi-Info 6 (WHO, Communicable Diseases Center), based on an estimated prevalence of 2.5% with a 95% CI of 2.25% to 2.75%, the sample size required for the study was 15 000.11–18 With an expected response rate of 60%,26 a random sample of 25 000 individuals, comprising 15 000 Chinese, 5000 Malays, and 5000 Indians was obtained to yield the 9000 Chinese, 3000 Malays, and 3000 Indians required for the study.
Statistics
Age, gender, and race-specific prevalence rates for stroke were derived; 95% CIs were calculated using the binomial distribution. The crude rates were back-weighted proportionately according to the racial distribution of Singapore23 and standardized to the WHO world population.27 Logistic regression analysis was performed using stroke as the outcome and demographic factors as explanatory variables. Data were analyzed using the Statistical Analysis System (SAS) version 8.0.
Ethics
The study was approved by the Ethics Committee of the hospital. Signed informed consent was obtained from all participants.
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Results |
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Descriptive Data
Of the sample of 24 978 individuals, 3994 individuals declined to participate, and 3379 remained noncontactable. A total of 2699 were ineligible, because they had moved or would be away for extended periods(1693), died (312), or their dwelling demolished (173). The final number of Phase I participants was 14 906, yielding a participation rate of 66.9%.
Study participants comprised 6734 men and 8172 women, mean age 63.4 years (SD 9.1 years), range 52.0 to 106.0 years, with 8906 Chinese, 3074 Malays, and 2926 Indians. Mean age of participants was higher than nonparticipants (62.9 years, P<0.0001). A total of 45.2% of participants were male, compared with 60.0% of nonparticipants (P<0.0001).
Of 2880 Phase II–eligible participants, 2487 (86.3%) were reviewed by study clinicians; 324 (11.3%) could not be examined but had data after medical records review. Only 69 (2.4%) had neither medical review nor medical records available.
Prevalence Rates
A total of 606 participants were diagnosed to have had a stroke, yielding a crude prevalence rate of 4.05% (95% CI, 3.75 to 4.38) and an age and gender-standardized rate of 3.65% (95% CI, 3.36 to 3.96; Table 1). Prevalence among adults aged 65 years was 7.67% (95% CI, 6.97 to 8.44).
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Prevalence of stroke was 1.5x higher among men compared with women, 4.53% (95% CI, 4.05 to 5.07) versus 2.91% (95% CI, 2.57 to 3.29), P<0.01. Prevalence rose with age, with prevalence among those >85 years being 22x that of those aged 50 to 54 years (P<0.001 for trend). The rise in prevalence with age was seen in both men and women (Table 1).
Inter-Racial Comparisons
The crude prevalence rate of stroke among Chinese, Malays, and Indians was similar at 4.30% (95% CI, 3.90 to 4.74), 3.74% (95% CI, 3.13 to 4.47), and 3.69% (95% CI, 3.07 to 4.44), respectively, P>0.2. Age and gender-standardized rates were similar, too: 3.76% (95% CI, 3.38 to 4.17), 3.32 (95% CI, 2.72 to 4.07), and 3.62% (95% CI, 2.95 to 4.44), respectively (P>0.2; Tables 2, 3, and 4 
).
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Among the Chinese, stroke prevalence was higher among men (P<0.01). A gender difference was not found among the Malays and Indians, possibly because their smaller sample size could not enable detection of such a difference. Prevalence rose with age among all 3 races (P<0.001 among Chinese and Indians, P<0.01 among Malays).
The highest age-standardized prevalence was among Chinese men at 4.78% (95% CI, 4.14 to 5.50) and lowest among Malay women at 2.81% (95% CI, 2.08 to 3.81), P=0.01. After adjusting for the number of comparisons made using the Bonferroni test, this difference remained statistically significant (P=0.01).
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Discussion |
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This is the first report of stroke prevalence in a multiracial Asian population. Older studies in various populations showed that stroke prevalence for all age groups combined varies between 0.4% and 2.0%; more recent studies showed a narrower range of 0.5% to 1.0%.2 We found a fairly high age- and sex-standardized rate of 3.65% among adults aged
50 years. The prevalence of 7.67% for adults aged 65 years is slightly above the 4.61% to 7.33% reported in the recent review.2 Figure 1 shows the age-specific rates in this study compared with other community-based studies.3,5,7,11,12,14,17 Prevalence rose exponentially with age in all studies This rise is not unexpected, because the strongest risk factor for stroke is age. The rate, however, fell in the oldest age group.7,12,16 This could be because of the smaller sample size in these higher age groups, widening the uncertainty around the prevalence rate.
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Among subjects aged >60/65 years, prevalence was highest in Singapore compared with other publications involving Chinese and Indians but similar to Japanese in Daisen (Figure 1).10–15,17 All these studies but one14 were door-to-door surveys in selected communities, recruiting 3896 to 25 8576 subjects. The WHO protocol24 or a derivative was used for screening, and the WHO definition25 used to diagnose stroke. Participation rate ranged from 62.3% to 100%. Differences in prevalence may be because of better case ascertainment in this study as a self-report of stroke was included in the screening questionnaire. Environmental factors leading to an increased frequency of stroke risk factors, such as hypertension, diabetes mellitus, and hyperlipidemia, may be a reason for the increased prevalence. Genetic factors alone are a less likely explanation, because the ancestors of Singaporean Chinese and Indians come from southern China and India. Finally, this is a very recent study, and the population may have benefited from newer stroke treatments, leading to falling stroke mortality and higher prevalence rates.22
Prevalence of stroke in this study is higher among men across all age groups, similar to most studies2–7,9–18 This may be related to the higher incidence of stroke among men compared with women, possibly from differences in the frequency and control of stroke risk factors such as hypertension.7,9 A few studies have shown higher rates in women in the highest age bands3–5,7,17,18 which have been attributed to poorer management of hypertension among women.18
Few community-based studies have been performed in southeast Asia, home to 443 million people of diverse origins.28–30 Crude prevalence rate was 1.12% among 3036 elderly Thais in rural areas,28 age-adjusted rate was 0.6% among 57649 south Vietnamese,29 and 0.5% among 2073 Indonesian30 city dwellers aged 25 to 64 years. In all studies, prevalence rose with age. Although these data are not age or sex-standardized, they are lower than that seen in this study. This may be because of lower incidence or higher mortality among stroke victims living in these developing countries or suboptimal case ascertainment. Genetic factors may also play a role as Thais, Vietnamese, and Indonesians may be genetically different from Chinese, Malays, and Indians.
Most prevalent studies were performed in relatively racially homogenous populations.3–7,9–18,28–30 Studies involving black and white subjects showed that the prevalence of stroke was highest among black men in the 1960s and 1970s19,20 and highest among black women in the 1970s and 1990s.21 Although genetic differences may have a role, the higher prevalence of stroke among blacks has been attributed to their higher frequency of hypertension and diabetes.31
There are no previous studies comparing stroke prevalence among ethnic groups in Asia. There is also no previous publication of stroke prevalence among Malays, who have distinct social, cultural, and genetic roots compared with Chinese and Indians. This study has shown that the prevalence is highest among Chinese men and lowest among Malay women (Figure 2). Although there are no data on the incidence of stroke among elderly Singaporeans, Malay women have the highest stroke incidence among adults aged <65 years32 and the highest stroke mortality.33 Malays have the highest smoking and obesity rates34 and are underrepresented in hospital-based stroke studies.35 The complex interplay between genetics, vascular risk factors, and health-seeking behavior and their impact on stroke incidence and mortality may explain the differing stroke prevalence among Singapore men and women of the 3 main races.
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This study has some limitations. The response rate was only 67%. It is unclear if people with stroke are more or less likely to participate; this can lead to under or overestimation of prevalence. As stroke is more common among men, the proportionately fewer male participants compared with male nonparticipants may lead to an underestimation. Some stroke cases may have slipped through the screening questionnaire or died before they could be interviewed, resulting in underestimation. Some Phase II–eligible subjects could not be examined, and diagnosis of stroke was made based on medical records in 11.3%, with no data in 2.4%, introducing a selection bias.
This study shows that prevalence of stroke in Singapore is comparable, if not a little higher, than similar studies among other populations. Prevalence rises with age and is higher among men. This article reports for the first time prevalence among Chinese, Malays, and Indians living in a single large community. Prevalence is lowest among Malay women despite their high stroke incidence and mortality. More studies need to be performed so as to confirm these findings and to better explain racial differences in stroke in Singapore.
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Acknowledgments |
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This project was jointly funded by the National Medical Research Council, Singapore, grant No. NMRC/0009/2000 and National Healthcare Group, Singapore, grant No. NHG BRG/01003. This work was possible through the participation of the residents in the study area, whom we gratefully acknowledge.
Received February 24, 2004; revision received August 23, 2004; accepted October 4, 2004.
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