The Epidemiology and Spatial Analysis of Stroke in Trinidad and Tobago in the First Decade of the 21st Century (2000-2009) ()
1. Introduction
The first global estimate on the burden of 135 diseases was provided by the 1990 Global Burden of Disease (GBD) study which showed that cerebrovascular diseases ranked as the second leading cause of death after ischemic heart disease [1] . In 2001, it was estimated that cerebrovascular accident (CVA/stroke) was the second leading cause of death globally, accounting for 5.5 million deaths worldwide, or 9.6% of all deaths, with approximately 70% occurring in low and middle income countries [2] . More recent the GBD study 2010 showed that although age-standardised rates of stroke mortality have decreased worldwide in the past two decades, the absolute number of people who have a stroke every year, stroke survivors, related deaths, and the overall global burden of stroke (DALYs lost) are great and increasing [3] . It is remarkable that there are very few stroke studies outside of the developed world when data are indicating that the majority of strokes are occurring in developing countries. High quality health statistics are essential for planning and implementing health policy in any country. In this regard, WHO developed an international stroke surveillance system called the “STEP wise” approach to stroke surveillance (STEPS-stroke) [4] . This approach forms a framework for surveillance and data collection for all WHO Member States. The first (step 1) of the three steps is the collection of information on stroke patients admitted to heath facilities. The benefits of this activity include providing evidence of the magnitude of stroke, identification of segments of the populations at risk and monitoring trends over time. In respect to the latter, the last study to report on CVA from Trinidad was for the period 1994-95 by Mahabir et al. [5] . They reported 1105 hospital admissions with the diagnosis of stroke for the one year period. In addition, the hospital case-fatality rate was 29%. The median length of stay was 4 days, with an interquartile range of 2 to 9, and accounted for approximately 9478 beds per annum, thus emphasizing that stroke in Trinidad in the 1990’s was a major public health challenge. Several modifiable risk factors were also identified and the need for effective preventative strategies was recommended.
Many risk factors for stroke have been described. These risk factors may be classified as biological (e.g. age and gender), physiological (e.g. high blood pressure), serum cholesterol, and fibrinogen levels, lifestyle behaviours (e.g. smoking, diet, alcohol consumption), and physical inactivity as well as social and environmental factors (e.g. education, social class and geography) [6] . Epidemiological research has shown that elevated blood pressure is the single most important risk factor for ischemic stroke with a population attributable fraction of 50% [7] . Further anti-hypertensive treatment has been shown to reduce stroke risk by 38 % [8] [9]
The aim of this study therefore is to determine the changing pattern of stroke in Trinidad and Tobago over the first decade of the 21st century. In addition, we investigated demographic factors, subtype of stroke, cardiovascular risk factors, and geographic distribution of patients presenting with stroke at the San Fernando General Hospital during the period 2000-2009.
2. Methods
WHO defines stroke as ““rapidly developing clinical signs of focal (or global) disturbance of cerebral function, with symptoms lasting 24 hours or longer or leading to death, with no apparent cause other than of vascular origin” [10] . By applying this definition transient ischemic attack (TIA), which is defined to last less than 24 hours, and patients with stroke symptoms caused by subdural hemorrhage, tumors, poisoning, or trauma will be identified and excluded from the analysis. However for the purposes of this study, stroke was clinically defined as the sudden onset of a focal neurological deficit of a presumed vascular etiology and lasting more than 24 hours. This was the single important entry criterion for the study. Accepted standards that are predated were used to diagnose stroke and stroke subtypes that included clinical, laboratory and non-invasive imaging and vascular studies, cardiac evaluation and information from autopsy studies. This included all ischemic and hemorrhagic strokes. The two ischemic stroke subtypes used are: atherothrombotic brain infarctions (ABI) and cardioembolic infarctions (CE), and the two hemorrhagic stroke subtypes are: intra-cerebral haemorrhages (ICH) and subarachnoid haemorrhages (SH). The neurological deficits found while examining an acute phase of stroke while it occurred was used to define the severity of the stroke. This definition was then broken down into four categories: none (no deficit), mild (deficit present in visual, motor, sensory or language domains but without functional impairment), moderate (deficit requiring assistance in one of the domains mentioned above), and severe (deficit requiring assistance in at least two of the domains). The 28-day case-fatality is a common parameter for the short-time survival in stroke patients [11] . Stroke patients who died within 29 - 180 days from the beginning of a stroke defined the long term case-fatality rate.
We used a retrospective incident case series design. The population for this study is all patients admitted to San Fernando General Hospital for the period 2000-2009 with a physician diagnosis of stroke. We aimed to achieve a sample size of approximately 1000 stroke patients. The San Fernando General Hospital was specifically chosen to allow comparison with the study reported by Mahabir and colleagues in 1998. The starting point of the study was a review of admission log books from all the respective wards admitting patients with stroke. All patients identified through this method had their unique hospital identification number, name and date of admission extracted. This information was used to retrieve all patients’ medical records. Each medical record was carefully reviewed by two independent investigators to ensure that all patients met the entry criterion. All socio-demographic and clinical data were then extracted from the patient’s medical record. All data was stored and password protected using a pin available only to investigators in SPSS version 16.Means and SDs were used to describe patients’ characteristics. Categorical variables were compared using the χ2 test and a 2-tailed P < 0.05 was considered statistically significant.The protocol for the study was approved by the University of West Indies Ethics Committee.
3. Results
During the period 2000-2009, 798admissions with a diagnostic label of CVA, Cerebral hemorrhage, TIA and brain stem infarct were carefully reviewed. Using the definition for TIA by the joint American Heart Association/American Stroke Association Stroke CouncilAmerican and other societies [11] , 70 patients were classified as having a TIA and were subsequently excluded from the analysis. Thus, 728 patients (369 males and 359 females) were classified as having a first-ever stroke. All patients were crossed checked to ensure that only the first event for stroke was recorded, and that repeated admissions over the period were not counted as an event.
The mean age of occurrence of a stroke was 66 ± 12.4 years; there were marginally more males (51%) females. Ischemic stroke was the most frequent subtype (48%) followed by intracerebral hemorrhage (15%), and undetermined stroke (37%), Table 1. TIA which was not included in the analysis represented 8.7% of admissions. The largest proportion of patients (30%) was seen in the age group 60 - 69, Figure 1. Case fatality rate (using the MONICA definition: the proportion of events that are fatal within 28 days of onset) was 23.5% [12] .
In Trinidad there are two major ethnic groups Africans and South East Asians (SEA) each representing 40% of the population. There was a significant (χ2, p < 0.05) ethnic disparity in the occurrence of stroke among SEA (53%) compared to Africans (27%). Further analysis Table 2, shows hospital admission rates according to age, gender and the number of strokes in each ethnic group. For every age group among men the admission rates were higher in SEA than in Africans. Similarly for every age group except ≥ 80 years stroke occurred more frequently among SEA than Africans. The admission rate for those of mixed ethnicity was significantly lower than those for SEA and Africans, for both male and female cases within all age groups. The highest number of first time stroke cases in African males was 33 while in South-East Asian males it was 60, both occurring in the age group 60 - 69 years. In African females, the largest number of first time stroke cases was 30, occurring in the age group ≥80 years, while the equivalent for SEA women was 59, occurring in the age group 60 - 69 years.
The trend in stroke admission over the 10 year period 2000-2009 is displayed in Figure 2, apart from the years 2005 and 2006 labeled red there was an overall increase of stroke with time. In fact there was more than a 50% increase in cases in 2000 compared to 2009.
The major risk factors associated with stroke are listed in Table 3. Hypertension and Diabetes were the major
Figure 1. The percentage distribution of stroke cases by age-group and gender.
Figure 2. The distribution of the number of cases of stroke by year.