Stroke Incidence and Case Fatality Rate in an Urban Population Marvin Okon, MD,* Nathaniel I. Adebobola, PhD,† Soyinka Julius, PhD,‡ Obembe Adebimpe, PhD,* Akinwole O. Taiwo, MD,x Akanni Akinyemi, PhD,jj and Nathaniel I. Thomas, PhD{
Background: The epidemiology of stroke in sub-Saharan African populations and variation of subtypes between communities are not well understood. Our aim was to ascertain prospectively the incidence of first-ever stroke and ischemic stroke subtypes in an urban city population of Southwestern Nigeria. Methods: A community-based stroke registry was set up to enroll hospitalized and nonhospitalized first-ever stroke cases at all health care facilities located in the assigned community. The study was conducted between November 1, 2010, and October 31, 2011, in Akure North and South Local Government Areas of Ondo State, Southwestern Nigeria. Results: We identified 298 incidents of strokes in patients presenting for the first time ever. Pathologic diagnosis was confirmed in 75% of the cases. Adjusted age-standardized incidence rate was 60.67 per 100,000 per year after adjustment to the World Health Organization World Population. Incidence of cerebral infarction and intracerebral hemorrhage increased with age in both men and women. Conclusions: The incidence of stroke in our population-based study ranks low compared with high-income countries. However, when incidence rates were compared by pathologic type, our rates for intracerebral hemorrhage and that of subarachnoid hemorrhage are comparable with those of high-income countries. Key Words: Stroke incidence—first-ever stroke—intracerebral hemorrhage—subarachnoid hemorrhage—cerebral infarct. Published by Elsevier Inc. on behalf of National Stroke Association
Significant mortality in sub-Saharan Africa is widely known to originate from infectious diseases such as human immunodeficiency virus/acquired immune deficiency syndrome and malaria. Several lines of evidence
From the *Faculty of Health Sciences, Obafemi Awolowo University, Ile-Ife, Nigeria; †North Greenville University Tigerville, South Carolina; ‡Faculty of Pharmacy, Obafemi Awolowo University, Nigeria; xUniversity of Alabama, Alabama; jjObafemi Awolowo University, Ile-Ife, Nigeria; and {University of South Carolina School of Medicine, Greenville, South Carolina. Received May 20, 2014; revision received October 13, 2014; accepted November 9, 2014. There is no financial disclosure on this study. Address correspondence to Nathaniel I. Thomas, PhD, University of South Carolina School of Medicine, Greenville, SC 29605. E-mail: [email protected]. 1052-3057/$ - see front matter Published by Elsevier Inc. on behalf of National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2014.11.004
now indicate that the incidence of stroke in Africa is on the increase1-5 and accounts for about .9%-4% of all hospital admissions and 2.8%-4.5% of total deaths.5 Whereas, an increase in the trend of incidence rates of stroke has been reported in low-income countries, there is a 42% decrease in stroke incidence in high-income countries. Indeed, the overall stroke incidence rate in low-income countries was reported to exceed the level observed in high-income countries by 20% in 2008. Although the actual incidence of stroke in Nigeria has not been established, recent studies indicate that the incidence rate is likely to be high, comparable with that of other African countries such as South Africa,1 Togo, and Tanzania.6 In addition, a striking difference in the incidence of stroke has also been observed in both gender and different demographics.7 In the present study, we established a community-based registry in Akure South and North Local Government Areas in Ondo State of Southwestern Nigeria. We enrolled hospitalized and
Journal of Stroke and Cerebrovascular Diseases, Vol. 24, No. 4 (April), 2015: pp 771-777
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nonhospitalized first-ever stroke patient presenting at any of the health care facilities located in the assigned communities as at the time of the study. The aim of this study was to investigate stroke incidence by age, sex, stroke subtype, and case fatality rate in first-ever stroke patients. We report the incidence of first-ever stroke, 30-day case fatality rates of the major stroke subtypes, and gender differences in a geographically defined region of a selected urban city of Nigeria.
Methods The project is a community-based stroke registry for first-ever stroke cases that occurred between November 1, 2010, and October 31, 2011. The city of Akure is located at 7.2500 N, 5.1950 E, and covers about 331 km2. It has a population of about 491,033 consisting of 245,198 males and 245,835 females.8 The people belong to the Yoruba ethnic group. The study was conducted in Akure South Local Government and Akure North Local Government Areas in Ondo State. Both the Local Government Areas comprises a mixed-income urban locality with a population of approximately 484,798, based on the data from the National Population Commission. We obtained the physical maps showing the demarcations for data enumeration area and street designations from the regional office of the National Population Commission. Before data collection, we reviewed the membership records of the Association of Private and General Medical Practitioners and also the Nigerian Medical Association to identify health care providers registered in the study area. In addition, we identified traditional medicine practitioners in the data collection areas. Once we identified the sites for the recruitment of strokes, letters were sent to the health care providers as an invitation to participate in the project. In the letter of invitation, we provided a detailed description and the objectives of the registry. We included information booklet listing the signs and symptoms of stroke, which would assist investigators to identify symptoms indicative of stroke. We identified a clinician who represents a local person in each health care facility and obtained their telephone contacts. Most telephone communication was via mobile/cell phones. In each health care facility, posters containing the registry contact phone numbers and names were mounted at strategic locations. These posters also located inside the consulting rooms and the doctors’ lounges in the health care facility served as a reminder to call the registry. The World Health Organization STEPwise approach to Surveillance (STEPS) stroke surveillance study provided the framework for our study. We followed only the STEP 1 study, and only hospital-based stroke data were collected (ie, events in health facilities). The first module contains information such as age, gender, identification of whether it is a first-time or recurrent stroke, and vital status (dead or alive) at discharge from hospital. The severity of stroke
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and the functional ability after the stroke were evaluated in the second module. The third module classified the pathologic subtypes of stroke. We evaluated suspected stroke incidence by first obtaining information from the local person who provided information for a potential stroke present at the health care facility. The local person sends the information to the teaching hospital. The local person obtains permission (verbally) from the patient to participate in the project, including biodata of the patients and permission for an evaluation in the hospital or a home at the patient’s convenient time. Our representative from the registry visited the identified stroke patients for evaluation either in the hospital or in their homes as the case may be. However, patients were evaluated only after information consent to participate in the project has been taken. Within the next 48 hours of the stroke incidence, the attending neurologist from the registry office visits the patient for further neurologic evaluation to confirm the diagnosis of stroke in the identified patients. Designated field assistants contacted health care providers’ facilities every week by telephone to inquire about cases of suspected stroke. In cases of nonhospitalized but suspected stroke, investigators contacted the family and examined the patient at home. Our trained field assistants surveyed all the designated enumeration areas. Data were collected for 5 weeks between September and October 2010 from all the health care delivery facilities, including private hospitals, clinics, maternity homes, and government-owned primary health care centers, and general hospitals.
Case Determination and Ascertainment We designed the study using the criteria for studies of stroke incidence, proposed by Sudlow and Warlow.9 We attempted to identify all cases of stroke without bias toward hospital admission or outpatient referral and to obtain brain computed tomography (CT) for every patient as soon as possible. A pilot study was conducted for 6 months in 2009 to determine the methods and practicability of the study. We held frequent meetings during the pilot phase and every 3 months thereafter with the general practitioners of private hospitals and public outpatient clinics and with residents, neurologists, and cardiologists. We collaborated with the local physicians (residents, cardiologists, and neurologists) who notified us of patients suspected to have stroke. If a patient is suspected of a stroke, the patient was immediately examined and hospitalized. Hospitalized patients were examined soon after admission by the attending neurologists and were monitored frequently until discharge. CT scans were done as soon as possible but primarily during the first week after stroke onset. All CT scans were later checked manually in a blinded manner by a neuroradiologist and the attending neurologists to ensure inclusion of all
CASE FATALITY RATES OF THE MAJOR STROKE SUBTYPES IN NIGERIA
patients not seen or referred to the study neurologists. We checked many cases prospectively from overlapping sources. Daily checks were done on emergency consultation and admission records in the hospitals including discharge lists. To identify all admitted patients, we conducted daily checks of admission and discharge lists for the government (general) hospital and weekly checks for the private hospitals to obtain medical records for patients with stroke or suspected stroke who were not transferred to the hospitals. Medical wards, intensive care units, and neurosurgical beds were checked weekly for any patient not referred to our study physicians. We contacted local physicians and private family practitioners every month by telephone to ask about patients with suspected stroke. In the case of patients with suspected stroke who were not hospitalized, one of the investigators contacted the family and examined the patient at home. Physicians were kept informed through a pocket card that provided information about phone numbers for referrals including signs and symptoms of stroke. Patients who were admitted and those referred to outpatient clinics were examined as soon as possible. A structured neurologic examination and CT were done for all patients who were alive at the time of identification. An investigator reviewed the medical records of those patients identified through other sources, and relevant clinical information such as radiologic information was extracted. All radiologic data were reviewed by a radiologist who was aware of the clinical signs and symptoms. Clinical notes and death certificates were checked when appropriate and available. All clinical and radiologic images and data were reviewed by the neurologist who categorized the patients by case, pathologic subtype, infarct subtype, and cause, according to prespecified definitions. Cases/patients were defined as individuals who had a stroke with a permanent address in the city during the study period. This helped us to exclude visitors in our study. We defined patients of first ever in a lifetime stroke as individuals without a clinical history of stroke independent of CT findings. Patients with a history of transient ischemic attack who had a subsequent stroke were regarded as incident stroke cases, those with a history of stroke and a subsequent transient ischemic attack were deemed recurrent cases, and those with incident stroke or recurrent stroke were categorized as any stroke cases. A stroke was defined as rapidly developed signs of focal (or global) disruptions of cerebral function lasting beyond 24 hours (unless interrupted by death), with no apparent nonvascular cause.10 Transient ischemic attack was defined as an acute loss of focal, cerebral, or ocular function with symptoms lasting less than 24 hours after adequate investigation was assumed to be a result of embolic or thrombotic vascular disease.11,12 We categorized intracerebral hemorrhage as cases of stroke on whom brain CT was done less than 30 days from symptom, and onset revealed an area of high
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attenuation in a region compatible with clinical signs and symptoms.13,14 We described subarachnoid hemorrhage as cases with acute onset of severe headache, sometimes associated with loss of consciousness, seizures, or focal neurologic signs such that when a brain CT scan was performed, it reveals subarachnoid or cisternal high attenuation.15,16 For those not hospitalized, we used information from notifications of the teaching hospitals or medical centers and attending physicians. Finally, subjects were enrolled in the study in one of the following ways: (1) medical records for hospitalized subjects; (2) notifications from private family physicians; (3) medical records from health centers; and (4) death certificates.
Data Analysis Using the data from our registry, we computed crude incidence rates by both genders separately and combined for the population using 95% confidence interval (CI). The denominator was the total base population for each Local Government Area for each city by the National Population Commission. We determined the age-adjusted rates using the direct method and adjusted to the current World Health Organization New World Population.17 In addition, we computed CI for crude rates and also for rates specific for age and sex on the assumption of a normal distribution. All analyses were done using JMP Pro 11.0 (SAS Institute Inc. Rockville, MD).
Results A total of 380 patients with possible events were initially considered for the study. After careful review, 82 patients were excluded. In particular, 40 of the 82 excluded patients were not local residents, 30 patients were excluded for some other clinical conditions, and 12 died during hospitalization. Therefore, between November 1, 2010, and October 31, 2011, a total of 298 first-ever strokes cases were registered. Our data (Table 1) comprise 184 men (61.74%) and 114 women (38.26%). Crude incidence of first-ever stroke was 60.69 (298 of 491,033) per 100,000 population (95% CI, 44.2-57.3) and 60.67 per 100,000 when adjusted to the world populations (Table 2). Tables 3 and 4 list the age- and sex-specific incidence rates by pathologic types. We identified 298 stroke incidences, and diagnosis was confirmed pathologically in 224 patients (75.17%), whereas 74 cases were undetermined. Incidence of stroke by infarct subtype was significantly greater in men than in women (P , .001), and increased for all stroke pathologic types, with the exception of subarachnoid hemorrhage (P , .001). Adjusted rates for case fatality for cerebral infarction was 54.30 per 100,000 per year, 48.72 per 100,000 per year for intracerebral hemorrhage, and 6.51 per 100,000 per year for
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Table 1. Age- and sex-specific incidence rates of first-ever stroke per 100,000 person-years in Akure, Southwestern Nigeria (2010-2011)
Sex/age, y, men 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages Women 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
Events, n
Person-years
Incidence
95% CI
Weighted rate (crude rate 3 specific rate)
95% CI
3 4 6 18 37 70 46 184
68,139 85,289 19,297 29,849 17,178 14,277 11,169 245,198
4.40 4.68 31.89 60.12 21.5 49.17 41.78 75.04
2.8-10.1 3.1-8.4 0-68.2 37.1-17.4 12.1-48.1 19.3-45.4 17.2-38.2 23-145
1.22 1.63 2.45 7.3 1.51 2.87 1.90 18.91
61.51 61.71 62.83 64.73 63.63 63.92 64.02 65.45
2 2 5 14 22 48 21 114
55,767 46,815 30,809 39,803 29,916 30,813 11,912 245,835
3.59 4.27 16.23 35.17 73.54 155.78 176.29 46.4
7-18.3 7-42.4 20-29.6 23-139 28-254 134-578 45-237 13.8-136.7
.81 .81 2.03 5.70 8.95 14.93 8.52 41.76
61.21 61.27 61.56 63.84 64.06 66.16 6.12 66.12
Abbreviation: CI, confidence interval.
subarachnoid hemorrhage (Table 4). Case fatality rate was also reflected on 12 of 298 patients (4.02%) who died during hospitalization and determined at 30 days after stroke onset.
Discussion The present study provided some interesting information on epidemiology of stroke in Nigeria. In general, most knowledge on stroke has mainly focused on Eastern Europe and Northern America. There is very little known about incidence of stroke in sub-Saharan Africa. The present study shows a lower incidence rate of first-ever stroke cases, compared with studies conducted in Oxfordshire in Europe,18 South America,19 and South
Asia.20 However, these data are hardly comparable because of the difference in the methodology used in various studies and the specific health system of each country. Our standardized incidence rate is higher than that of a recent study in Nigeria.2 In the last few years, the Nigerian stroke registries have reported variable crude- and age-adjusted stroke incidence rates.7 Studies on incidence of strokes are very few in Nigeria, and comparison between existing studies is difficult. The existing studies in Nigeria differ in case ascertainment differences and in terms of methods by which the type of stroke was assessed, either by CT scan or a validated clinical score or the combination of both. Our present study contributes to the existing population-based study, with an inclusion of ischemic strokes as the basis of the most likely
Table 2. Combined (male and female) incidence and adjusted rates of stroke by age, sex, and per 100,000 person-years in Akure, Southwestern Nigeria
Sex/age, y
Incidence
95% CI
Weighted rate (crude rate 3 specific weight)
95% CI
0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
4.04 4.54 21.95 45.94 125.28 261.70 290.28 60.69
1.3-3.2 2.8-4.4 10.2-19.3 23.7-43.3 101-123.7 196.7-251.4 211.6-287.3 44.2-57.3
1.02 1.22 2.24 6.52 12.02 24.03 13.62 60.67
61.01 61.16 61.62 61.97 64.67 614.43 64.01 632.65
Abbreviation: CI, confidence interval.
CASE FATALITY RATES OF THE MAJOR STROKE SUBTYPES IN NIGERIA
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Table 3. Pathologic stroke types incidence by age, sex, and per 100,000 person-years in Akure, Southwestern Nigeria Infarction Sex/age, y Men 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages Women 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
Intracerebral hemorrhage
Subarachnoid hemorrhage
n
Rate
95% CI
n
Rate
95% CI
n
Rate
95% CI
1 2 4 12 25 20 30 94
1.47 2.34 2.73 4.20 14.54 14.09 26.60 38.34
2.4-13.8 3.1-32.2 7.6-10.1 4.1-5.9 15.2-25.1 21.9-78.2 31.8-131.3 32.6-414.7
1 1 2 4 8 7 6 29
1.46 1.17 10.36 13.40 46.57 49.02 53.72 11.82
.10-21.7 .08-17.9 1.6-52.1 10.3-58.6 34.2-112.5 26.2-91.2 47.8-68.9 15.03-52.3
1 1 1 2 2 1 1 9
1.47 1.18 5.18 6.7 11.64 7.00 8.94 3.67
.09-19.3 .09-19.8 .10-20.6 2.8-17 1.7-24.4 1.5-11.7 3.0-32.1 3.2-111.4
1 1 2 7 15 18 14 58
1.79 2.14 6.49 17.59 50.14 58.15 117.53 23.59
.3-7.9 .10-20.6 3.1-32.6 14.2-54.3 15.1-64.2 65.3-87.4 130.4-217.0 24.1-234.3
1 1 2 6 4 5 6 25
3.58 4.27 12.98 25.12 40.11 6.49 100.73 17.99
.08-17.5 1.5-15.2 7.3-22.4 14.5-55.7 7.7-55.6 16.8-105.7 60.3-187.7 .3-24.9
1 1 1 1 5 1 1 11
3.54 4.28 6.51 7.53 23.40 6.46 6.98 8.13
.2-7.4 .08-17.8 .11-21.8 2.6-4.32 .30-22.5 .09-18.6 1.7-15.5 3.5-97.9
Abbreviation: CI, confidence interval.
in our study centers are transported to other medical centers outside the study areas. A couple of other factors may as well contribute to the low ratio in the present study. It is important to point out that because we restricted the present study to first-ever stroke, this may result in a lower ratio compared with routine stroke mortality statistics. It is also important to point out that assessment of mortality was difficult in this study, especially, when outside of hospitals. Although there are several ongoing studies on death registration in Nigeria,24,25 there has been no validation study yet. Death registration in Nigeria is widely acknowledged as poor, with an estimated over 40% of deaths unregistered, and more than 20% of those registered were classified as death due to an ill-defined
stroke mechanism. When incidence rates are compared by pathologic type, our standardized rate for intracerebral hemorrhage is comparably lower than that of Melbourne in Australia,21 Oxfordshire in the United Kingdom,13 Erlangen in Germany,22 South America,19 and South Asia.20 In addition, our standardized rate for cerebral infarction was low and ranks in the lower portion among studies reported from the International Stroke Incidence.23 Our finding that incidence rate for cerebral infarction was low explains the low overall stroke incidence rate because cerebral infarction is the most frequent subtype (62% in men and 38% in women). Our current result may reflect a true low incidence or fatality rates. It may also be because of under-reporting of cases. It is also possible that stroke patients who reside
Table 4. Pathologic stroke types incidence by age, sex, per 100,000 person-years in Akure, Southwestern Nigeria Infarction Sex/age, y
n
R
95% CI
0-34 2 1.61 1.6-3.22 35-44 3 2.27 7.8-24.6 45-54 6 11.97 10.2-24.7 55-64 19 27.27 11.5-29.2 65-74 40 84.93 34.1-50.2 75-84 38 84.27 45.3-76.3 .85 44 190.63 67.2-251.4 Total 150 30.54 47.5-265.3 Adjusted rate — — — Abbreviation: CI, confidence interval.
Intracerebral hemorrhage Weighted
n
R
.37296 2.28084 8.72049 11.05006 15.88461 12.01231 4.94991 — 54.3
2 2 4 10 12 2 12 54 —
1.62 1.51 7.98 14.35 25.48 4.4 51.99 10.99 —
Subarachnoid hemorrhage
95% CI Weighted
n
0-9 0-18 5-12 11-28 19-52 16-24 43-157 5-80 —
2 1.61 2.7-4.34 2 1.51 2.87-5.43 2 3.99 3.23-6.5 3 4.30 4.14-7.5 7 14.86 5.21-7.6 2 4.43 3.01-6.7 2 8.66 6.46-8.3 20 4.03 4-13 — — —
1.27782 3.45723 6.15221 5.89599 10.40294 12.7812 3.2976 — 48.72
R
95% CI
Weighted .88578 .93432 .98126 1.0751 .70829 1.02341 .48 — 6.51
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cause. Unregistration of deaths and unreliable attribution of causes of deaths are a major concern. Although the observed differences in our results compared with other studies23,27 could be linked to methodologic differences in case ascertainment, we also believe that presentation of the data in terms of ageand sex-specific or standardized results of stroke incidence differences in age and/or sex among study subjects are major factors that are worth mentioning. Mortality generally increased significantly in elderly patients with strokes compared with younger people.28 Age is one of the most important predictors of unfavorable stroke outcomes, and a significant correlation has been reported between age and stroke mortality.29 Stroke is most likely to represent major public health problem for the foreseeable future in an aging population as the incidence of stroke rises markedly with age.30 Case fatality for first-ever stroke episode was lower than that found in most other studies.31 Our finding supports the idea that initial efforts should be directed at decreasing the extent of brain damage caused by strokes, then followed by reducing the effects of impairments, and then the implementation of secondary prevention measures for cardiovascular deaths.29 We observed that acute phase of stroke is frequently inadequately managed in some of the centers in Nigeria. Our current observation is supported by previous studies.32 In addition, some stroke survivals do not have access to imaging for assessments in the acute phase of stroke because they could not afford the cost. Treatment options are also facilitated by faith healing that considers cultural and religious beliefs. Patients and relatives often consult faith healers because they provide cultural and theoretical familiarity by complying with the desires and expectations of relatives/patients.33 The strength of the present study is our ability to identify as many stroke cases as possible with CT. Extrapolation of these data to other subSaharan African populations should be done with caution, and our findings need to be replicated in different locations. In summary, the overall distribution of major stroke subtypes is similar to that of other studies in different populations. Although there is some heterogeneity, however, even within Nigeria the incidence of different subtypes of stroke appears to vary. Precisely, the incidence rates of cerebral infarction and intracerebral hemorrhage among men and women were different in the present study. These differences may have occurred by chance, or because of the differences in case ascertainment methodology, or even because of the distribution of subtypes within the undetermined group. There are many possibilities why these presumed differences in incidence rates may occur. For instance, differences in lifestyle and ethnic combination, however, further research would be necessary to establish this with more certainty.
Acknowledgment: The authors would like to thank all of the registry investigators who helped in the registration process. We thank Dr Melinda Ingiaimo for editing the manuscript. We thank the Carnegie fellowship program that helped Dr Nathaniel I. Thomas to participate in this work.
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Background: The epidemiology of stroke in sub-Saharan African populations and variation of subtypes between communities are not well understood. Our aim was to ascertain prospectively the incidence of first-ever stroke and ischemic stroke subtypes in an urban city population of Southwestern Nigeria. Methods: A community-based stroke registry was set up to enroll hospitalized and nonhospitalized first-ever stroke cases at all health care facilities located in the assigned community. The study was conducted between November 1, 2010, and October 31, 2011, in Akure North and South Local Government Areas of Ondo State, Southwestern Nigeria. Results: We identified 298 incidents of strokes in patients presenting for the first time ever. Pathologic diagnosis was confirmed in 75% of the cases. Adjusted age-standardized incidence rate was 60.67 per 100,000 per year after adjustment to the World Health Organization World Population. Incidence of cerebral infarction and intracerebral hemorrhage increased with age in both men and women. Conclusions: The incidence of stroke in our population-based study ranks low compared with high-income countries. However, when incidence rates were compared by pathologic type, our rates for intracerebral hemorrhage and that of subarachnoid hemorrhage are comparable with those of high-income countries. Key Words: Stroke incidence—first-ever stroke—intracerebral hemorrhage—subarachnoid hemorrhage—cerebral infarct. Published by Elsevier Inc. on behalf of National Stroke Association
Significant mortality in sub-Saharan Africa is widely known to originate from infectious diseases such as human immunodeficiency virus/acquired immune deficiency syndrome and malaria. Several lines of evidence
From the *Faculty of Health Sciences, Obafemi Awolowo University, Ile-Ife, Nigeria; †North Greenville University Tigerville, South Carolina; ‡Faculty of Pharmacy, Obafemi Awolowo University, Nigeria; xUniversity of Alabama, Alabama; jjObafemi Awolowo University, Ile-Ife, Nigeria; and {University of South Carolina School of Medicine, Greenville, South Carolina. Received May 20, 2014; revision received October 13, 2014; accepted November 9, 2014. There is no financial disclosure on this study. Address correspondence to Nathaniel I. Thomas, PhD, University of South Carolina School of Medicine, Greenville, SC 29605. E-mail: [email protected]. 1052-3057/$ - see front matter Published by Elsevier Inc. on behalf of National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2014.11.004
now indicate that the incidence of stroke in Africa is on the increase1-5 and accounts for about .9%-4% of all hospital admissions and 2.8%-4.5% of total deaths.5 Whereas, an increase in the trend of incidence rates of stroke has been reported in low-income countries, there is a 42% decrease in stroke incidence in high-income countries. Indeed, the overall stroke incidence rate in low-income countries was reported to exceed the level observed in high-income countries by 20% in 2008. Although the actual incidence of stroke in Nigeria has not been established, recent studies indicate that the incidence rate is likely to be high, comparable with that of other African countries such as South Africa,1 Togo, and Tanzania.6 In addition, a striking difference in the incidence of stroke has also been observed in both gender and different demographics.7 In the present study, we established a community-based registry in Akure South and North Local Government Areas in Ondo State of Southwestern Nigeria. We enrolled hospitalized and
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nonhospitalized first-ever stroke patient presenting at any of the health care facilities located in the assigned communities as at the time of the study. The aim of this study was to investigate stroke incidence by age, sex, stroke subtype, and case fatality rate in first-ever stroke patients. We report the incidence of first-ever stroke, 30-day case fatality rates of the major stroke subtypes, and gender differences in a geographically defined region of a selected urban city of Nigeria.
Methods The project is a community-based stroke registry for first-ever stroke cases that occurred between November 1, 2010, and October 31, 2011. The city of Akure is located at 7.2500 N, 5.1950 E, and covers about 331 km2. It has a population of about 491,033 consisting of 245,198 males and 245,835 females.8 The people belong to the Yoruba ethnic group. The study was conducted in Akure South Local Government and Akure North Local Government Areas in Ondo State. Both the Local Government Areas comprises a mixed-income urban locality with a population of approximately 484,798, based on the data from the National Population Commission. We obtained the physical maps showing the demarcations for data enumeration area and street designations from the regional office of the National Population Commission. Before data collection, we reviewed the membership records of the Association of Private and General Medical Practitioners and also the Nigerian Medical Association to identify health care providers registered in the study area. In addition, we identified traditional medicine practitioners in the data collection areas. Once we identified the sites for the recruitment of strokes, letters were sent to the health care providers as an invitation to participate in the project. In the letter of invitation, we provided a detailed description and the objectives of the registry. We included information booklet listing the signs and symptoms of stroke, which would assist investigators to identify symptoms indicative of stroke. We identified a clinician who represents a local person in each health care facility and obtained their telephone contacts. Most telephone communication was via mobile/cell phones. In each health care facility, posters containing the registry contact phone numbers and names were mounted at strategic locations. These posters also located inside the consulting rooms and the doctors’ lounges in the health care facility served as a reminder to call the registry. The World Health Organization STEPwise approach to Surveillance (STEPS) stroke surveillance study provided the framework for our study. We followed only the STEP 1 study, and only hospital-based stroke data were collected (ie, events in health facilities). The first module contains information such as age, gender, identification of whether it is a first-time or recurrent stroke, and vital status (dead or alive) at discharge from hospital. The severity of stroke
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and the functional ability after the stroke were evaluated in the second module. The third module classified the pathologic subtypes of stroke. We evaluated suspected stroke incidence by first obtaining information from the local person who provided information for a potential stroke present at the health care facility. The local person sends the information to the teaching hospital. The local person obtains permission (verbally) from the patient to participate in the project, including biodata of the patients and permission for an evaluation in the hospital or a home at the patient’s convenient time. Our representative from the registry visited the identified stroke patients for evaluation either in the hospital or in their homes as the case may be. However, patients were evaluated only after information consent to participate in the project has been taken. Within the next 48 hours of the stroke incidence, the attending neurologist from the registry office visits the patient for further neurologic evaluation to confirm the diagnosis of stroke in the identified patients. Designated field assistants contacted health care providers’ facilities every week by telephone to inquire about cases of suspected stroke. In cases of nonhospitalized but suspected stroke, investigators contacted the family and examined the patient at home. Our trained field assistants surveyed all the designated enumeration areas. Data were collected for 5 weeks between September and October 2010 from all the health care delivery facilities, including private hospitals, clinics, maternity homes, and government-owned primary health care centers, and general hospitals.
Case Determination and Ascertainment We designed the study using the criteria for studies of stroke incidence, proposed by Sudlow and Warlow.9 We attempted to identify all cases of stroke without bias toward hospital admission or outpatient referral and to obtain brain computed tomography (CT) for every patient as soon as possible. A pilot study was conducted for 6 months in 2009 to determine the methods and practicability of the study. We held frequent meetings during the pilot phase and every 3 months thereafter with the general practitioners of private hospitals and public outpatient clinics and with residents, neurologists, and cardiologists. We collaborated with the local physicians (residents, cardiologists, and neurologists) who notified us of patients suspected to have stroke. If a patient is suspected of a stroke, the patient was immediately examined and hospitalized. Hospitalized patients were examined soon after admission by the attending neurologists and were monitored frequently until discharge. CT scans were done as soon as possible but primarily during the first week after stroke onset. All CT scans were later checked manually in a blinded manner by a neuroradiologist and the attending neurologists to ensure inclusion of all
CASE FATALITY RATES OF THE MAJOR STROKE SUBTYPES IN NIGERIA
patients not seen or referred to the study neurologists. We checked many cases prospectively from overlapping sources. Daily checks were done on emergency consultation and admission records in the hospitals including discharge lists. To identify all admitted patients, we conducted daily checks of admission and discharge lists for the government (general) hospital and weekly checks for the private hospitals to obtain medical records for patients with stroke or suspected stroke who were not transferred to the hospitals. Medical wards, intensive care units, and neurosurgical beds were checked weekly for any patient not referred to our study physicians. We contacted local physicians and private family practitioners every month by telephone to ask about patients with suspected stroke. In the case of patients with suspected stroke who were not hospitalized, one of the investigators contacted the family and examined the patient at home. Physicians were kept informed through a pocket card that provided information about phone numbers for referrals including signs and symptoms of stroke. Patients who were admitted and those referred to outpatient clinics were examined as soon as possible. A structured neurologic examination and CT were done for all patients who were alive at the time of identification. An investigator reviewed the medical records of those patients identified through other sources, and relevant clinical information such as radiologic information was extracted. All radiologic data were reviewed by a radiologist who was aware of the clinical signs and symptoms. Clinical notes and death certificates were checked when appropriate and available. All clinical and radiologic images and data were reviewed by the neurologist who categorized the patients by case, pathologic subtype, infarct subtype, and cause, according to prespecified definitions. Cases/patients were defined as individuals who had a stroke with a permanent address in the city during the study period. This helped us to exclude visitors in our study. We defined patients of first ever in a lifetime stroke as individuals without a clinical history of stroke independent of CT findings. Patients with a history of transient ischemic attack who had a subsequent stroke were regarded as incident stroke cases, those with a history of stroke and a subsequent transient ischemic attack were deemed recurrent cases, and those with incident stroke or recurrent stroke were categorized as any stroke cases. A stroke was defined as rapidly developed signs of focal (or global) disruptions of cerebral function lasting beyond 24 hours (unless interrupted by death), with no apparent nonvascular cause.10 Transient ischemic attack was defined as an acute loss of focal, cerebral, or ocular function with symptoms lasting less than 24 hours after adequate investigation was assumed to be a result of embolic or thrombotic vascular disease.11,12 We categorized intracerebral hemorrhage as cases of stroke on whom brain CT was done less than 30 days from symptom, and onset revealed an area of high
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attenuation in a region compatible with clinical signs and symptoms.13,14 We described subarachnoid hemorrhage as cases with acute onset of severe headache, sometimes associated with loss of consciousness, seizures, or focal neurologic signs such that when a brain CT scan was performed, it reveals subarachnoid or cisternal high attenuation.15,16 For those not hospitalized, we used information from notifications of the teaching hospitals or medical centers and attending physicians. Finally, subjects were enrolled in the study in one of the following ways: (1) medical records for hospitalized subjects; (2) notifications from private family physicians; (3) medical records from health centers; and (4) death certificates.
Data Analysis Using the data from our registry, we computed crude incidence rates by both genders separately and combined for the population using 95% confidence interval (CI). The denominator was the total base population for each Local Government Area for each city by the National Population Commission. We determined the age-adjusted rates using the direct method and adjusted to the current World Health Organization New World Population.17 In addition, we computed CI for crude rates and also for rates specific for age and sex on the assumption of a normal distribution. All analyses were done using JMP Pro 11.0 (SAS Institute Inc. Rockville, MD).
Results A total of 380 patients with possible events were initially considered for the study. After careful review, 82 patients were excluded. In particular, 40 of the 82 excluded patients were not local residents, 30 patients were excluded for some other clinical conditions, and 12 died during hospitalization. Therefore, between November 1, 2010, and October 31, 2011, a total of 298 first-ever strokes cases were registered. Our data (Table 1) comprise 184 men (61.74%) and 114 women (38.26%). Crude incidence of first-ever stroke was 60.69 (298 of 491,033) per 100,000 population (95% CI, 44.2-57.3) and 60.67 per 100,000 when adjusted to the world populations (Table 2). Tables 3 and 4 list the age- and sex-specific incidence rates by pathologic types. We identified 298 stroke incidences, and diagnosis was confirmed pathologically in 224 patients (75.17%), whereas 74 cases were undetermined. Incidence of stroke by infarct subtype was significantly greater in men than in women (P , .001), and increased for all stroke pathologic types, with the exception of subarachnoid hemorrhage (P , .001). Adjusted rates for case fatality for cerebral infarction was 54.30 per 100,000 per year, 48.72 per 100,000 per year for intracerebral hemorrhage, and 6.51 per 100,000 per year for
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Table 1. Age- and sex-specific incidence rates of first-ever stroke per 100,000 person-years in Akure, Southwestern Nigeria (2010-2011)
Sex/age, y, men 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages Women 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
Events, n
Person-years
Incidence
95% CI
Weighted rate (crude rate 3 specific rate)
95% CI
3 4 6 18 37 70 46 184
68,139 85,289 19,297 29,849 17,178 14,277 11,169 245,198
4.40 4.68 31.89 60.12 21.5 49.17 41.78 75.04
2.8-10.1 3.1-8.4 0-68.2 37.1-17.4 12.1-48.1 19.3-45.4 17.2-38.2 23-145
1.22 1.63 2.45 7.3 1.51 2.87 1.90 18.91
61.51 61.71 62.83 64.73 63.63 63.92 64.02 65.45
2 2 5 14 22 48 21 114
55,767 46,815 30,809 39,803 29,916 30,813 11,912 245,835
3.59 4.27 16.23 35.17 73.54 155.78 176.29 46.4
7-18.3 7-42.4 20-29.6 23-139 28-254 134-578 45-237 13.8-136.7
.81 .81 2.03 5.70 8.95 14.93 8.52 41.76
61.21 61.27 61.56 63.84 64.06 66.16 6.12 66.12
Abbreviation: CI, confidence interval.
subarachnoid hemorrhage (Table 4). Case fatality rate was also reflected on 12 of 298 patients (4.02%) who died during hospitalization and determined at 30 days after stroke onset.
Discussion The present study provided some interesting information on epidemiology of stroke in Nigeria. In general, most knowledge on stroke has mainly focused on Eastern Europe and Northern America. There is very little known about incidence of stroke in sub-Saharan Africa. The present study shows a lower incidence rate of first-ever stroke cases, compared with studies conducted in Oxfordshire in Europe,18 South America,19 and South
Asia.20 However, these data are hardly comparable because of the difference in the methodology used in various studies and the specific health system of each country. Our standardized incidence rate is higher than that of a recent study in Nigeria.2 In the last few years, the Nigerian stroke registries have reported variable crude- and age-adjusted stroke incidence rates.7 Studies on incidence of strokes are very few in Nigeria, and comparison between existing studies is difficult. The existing studies in Nigeria differ in case ascertainment differences and in terms of methods by which the type of stroke was assessed, either by CT scan or a validated clinical score or the combination of both. Our present study contributes to the existing population-based study, with an inclusion of ischemic strokes as the basis of the most likely
Table 2. Combined (male and female) incidence and adjusted rates of stroke by age, sex, and per 100,000 person-years in Akure, Southwestern Nigeria
Sex/age, y
Incidence
95% CI
Weighted rate (crude rate 3 specific weight)
95% CI
0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
4.04 4.54 21.95 45.94 125.28 261.70 290.28 60.69
1.3-3.2 2.8-4.4 10.2-19.3 23.7-43.3 101-123.7 196.7-251.4 211.6-287.3 44.2-57.3
1.02 1.22 2.24 6.52 12.02 24.03 13.62 60.67
61.01 61.16 61.62 61.97 64.67 614.43 64.01 632.65
Abbreviation: CI, confidence interval.
CASE FATALITY RATES OF THE MAJOR STROKE SUBTYPES IN NIGERIA
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Table 3. Pathologic stroke types incidence by age, sex, and per 100,000 person-years in Akure, Southwestern Nigeria Infarction Sex/age, y Men 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages Women 0-34 35-44 45-54 55-64 65-74 75-84 .85 All ages
Intracerebral hemorrhage
Subarachnoid hemorrhage
n
Rate
95% CI
n
Rate
95% CI
n
Rate
95% CI
1 2 4 12 25 20 30 94
1.47 2.34 2.73 4.20 14.54 14.09 26.60 38.34
2.4-13.8 3.1-32.2 7.6-10.1 4.1-5.9 15.2-25.1 21.9-78.2 31.8-131.3 32.6-414.7
1 1 2 4 8 7 6 29
1.46 1.17 10.36 13.40 46.57 49.02 53.72 11.82
.10-21.7 .08-17.9 1.6-52.1 10.3-58.6 34.2-112.5 26.2-91.2 47.8-68.9 15.03-52.3
1 1 1 2 2 1 1 9
1.47 1.18 5.18 6.7 11.64 7.00 8.94 3.67
.09-19.3 .09-19.8 .10-20.6 2.8-17 1.7-24.4 1.5-11.7 3.0-32.1 3.2-111.4
1 1 2 7 15 18 14 58
1.79 2.14 6.49 17.59 50.14 58.15 117.53 23.59
.3-7.9 .10-20.6 3.1-32.6 14.2-54.3 15.1-64.2 65.3-87.4 130.4-217.0 24.1-234.3
1 1 2 6 4 5 6 25
3.58 4.27 12.98 25.12 40.11 6.49 100.73 17.99
.08-17.5 1.5-15.2 7.3-22.4 14.5-55.7 7.7-55.6 16.8-105.7 60.3-187.7 .3-24.9
1 1 1 1 5 1 1 11
3.54 4.28 6.51 7.53 23.40 6.46 6.98 8.13
.2-7.4 .08-17.8 .11-21.8 2.6-4.32 .30-22.5 .09-18.6 1.7-15.5 3.5-97.9
Abbreviation: CI, confidence interval.
in our study centers are transported to other medical centers outside the study areas. A couple of other factors may as well contribute to the low ratio in the present study. It is important to point out that because we restricted the present study to first-ever stroke, this may result in a lower ratio compared with routine stroke mortality statistics. It is also important to point out that assessment of mortality was difficult in this study, especially, when outside of hospitals. Although there are several ongoing studies on death registration in Nigeria,24,25 there has been no validation study yet. Death registration in Nigeria is widely acknowledged as poor, with an estimated over 40% of deaths unregistered, and more than 20% of those registered were classified as death due to an ill-defined
stroke mechanism. When incidence rates are compared by pathologic type, our standardized rate for intracerebral hemorrhage is comparably lower than that of Melbourne in Australia,21 Oxfordshire in the United Kingdom,13 Erlangen in Germany,22 South America,19 and South Asia.20 In addition, our standardized rate for cerebral infarction was low and ranks in the lower portion among studies reported from the International Stroke Incidence.23 Our finding that incidence rate for cerebral infarction was low explains the low overall stroke incidence rate because cerebral infarction is the most frequent subtype (62% in men and 38% in women). Our current result may reflect a true low incidence or fatality rates. It may also be because of under-reporting of cases. It is also possible that stroke patients who reside
Table 4. Pathologic stroke types incidence by age, sex, per 100,000 person-years in Akure, Southwestern Nigeria Infarction Sex/age, y
n
R
95% CI
0-34 2 1.61 1.6-3.22 35-44 3 2.27 7.8-24.6 45-54 6 11.97 10.2-24.7 55-64 19 27.27 11.5-29.2 65-74 40 84.93 34.1-50.2 75-84 38 84.27 45.3-76.3 .85 44 190.63 67.2-251.4 Total 150 30.54 47.5-265.3 Adjusted rate — — — Abbreviation: CI, confidence interval.
Intracerebral hemorrhage Weighted
n
R
.37296 2.28084 8.72049 11.05006 15.88461 12.01231 4.94991 — 54.3
2 2 4 10 12 2 12 54 —
1.62 1.51 7.98 14.35 25.48 4.4 51.99 10.99 —
Subarachnoid hemorrhage
95% CI Weighted
n
0-9 0-18 5-12 11-28 19-52 16-24 43-157 5-80 —
2 1.61 2.7-4.34 2 1.51 2.87-5.43 2 3.99 3.23-6.5 3 4.30 4.14-7.5 7 14.86 5.21-7.6 2 4.43 3.01-6.7 2 8.66 6.46-8.3 20 4.03 4-13 — — —
1.27782 3.45723 6.15221 5.89599 10.40294 12.7812 3.2976 — 48.72
R
95% CI
Weighted .88578 .93432 .98126 1.0751 .70829 1.02341 .48 — 6.51
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cause. Unregistration of deaths and unreliable attribution of causes of deaths are a major concern. Although the observed differences in our results compared with other studies23,27 could be linked to methodologic differences in case ascertainment, we also believe that presentation of the data in terms of ageand sex-specific or standardized results of stroke incidence differences in age and/or sex among study subjects are major factors that are worth mentioning. Mortality generally increased significantly in elderly patients with strokes compared with younger people.28 Age is one of the most important predictors of unfavorable stroke outcomes, and a significant correlation has been reported between age and stroke mortality.29 Stroke is most likely to represent major public health problem for the foreseeable future in an aging population as the incidence of stroke rises markedly with age.30 Case fatality for first-ever stroke episode was lower than that found in most other studies.31 Our finding supports the idea that initial efforts should be directed at decreasing the extent of brain damage caused by strokes, then followed by reducing the effects of impairments, and then the implementation of secondary prevention measures for cardiovascular deaths.29 We observed that acute phase of stroke is frequently inadequately managed in some of the centers in Nigeria. Our current observation is supported by previous studies.32 In addition, some stroke survivals do not have access to imaging for assessments in the acute phase of stroke because they could not afford the cost. Treatment options are also facilitated by faith healing that considers cultural and religious beliefs. Patients and relatives often consult faith healers because they provide cultural and theoretical familiarity by complying with the desires and expectations of relatives/patients.33 The strength of the present study is our ability to identify as many stroke cases as possible with CT. Extrapolation of these data to other subSaharan African populations should be done with caution, and our findings need to be replicated in different locations. In summary, the overall distribution of major stroke subtypes is similar to that of other studies in different populations. Although there is some heterogeneity, however, even within Nigeria the incidence of different subtypes of stroke appears to vary. Precisely, the incidence rates of cerebral infarction and intracerebral hemorrhage among men and women were different in the present study. These differences may have occurred by chance, or because of the differences in case ascertainment methodology, or even because of the distribution of subtypes within the undetermined group. There are many possibilities why these presumed differences in incidence rates may occur. For instance, differences in lifestyle and ethnic combination, however, further research would be necessary to establish this with more certainty.
Acknowledgment: The authors would like to thank all of the registry investigators who helped in the registration process. We thank Dr Melinda Ingiaimo for editing the manuscript. We thank the Carnegie fellowship program that helped Dr Nathaniel I. Thomas to participate in this work.
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