In our study, 15.7% of stroke patients were rehospitalized due to recurrent stroke, and 58.3% of the patients survived after 5 years. A wide range of survival (29.0%-60.3%) and recurrent probabilities (9.4%-23.8%) have been reported cross different population [7–16], which could in part be explained by differences in study population, stroke subtypes, stroke severity, first-ever or recurrent stroke. Our results were within the reported range. IS patients had the highest survival rate, followed by ICH and then SAH patients in this study. Compared with IS and SAH patients, ICH patients were more likely to be hospitalized due to stroke recurrence after considering death as the competing risk. If competing risk of death was not considered, IS had highest risk of stroke recurrence, followed by ICH and SAH, which were tally with the reported findings [7–16]. Therefore adjustment of competing risk of death is crucial for studying the risk of stroke recurrence.
It is not surprise that older patients had higher risks of mortality and stroke recurrence in all stroke categories in this study. Gender did not significantly influence outcomes except IS in this study. After adjusting for admitting year, age, and ethnic group, females had a lower relative risk of mortality than males among IS patients. According to the National Health Survey conducted in year 2004 in Singapore , males had higher prevalence of DM, HTN, total cholesterol, and smoking compared to females. This may help explain the gender difference to some extend in this study. How gender affects the post-stroke survival was inconclusive based on published studies [17–21]. This discrepancy might be caused by sample size, stroke subtype, stroke severity, and confounders adjusted in the studies.
In our study, ethnic group didn’t influence the 5 year risk of mortality and stroke recurrence except for IS patients. There was an increased risk of mortality and stroke recurrence in Malays and other ethnic groups as compared with Chinese among IS patients. This trend may be partially explained by the higher load of atherosclerotic risk factors among them. Malays had higher prevalence of DM, lipids, and smoking compared to Chinese according to the National Health Survey 2004 . Differences in outcomes for various ethnic groups have also been reported in other studies [22–25].
We also examined the causes of death for patients with different subtypes of stroke. A large proportion of deaths were related to stroke complications. Complications of stroke can be classified in the cerebral and extra cerebral . Extra cerebral complications include pneumonia and pneumonitis, acute hypertensive response, venous thromboembolism, cardiac complications, urinary tract infections and decubitus ulcers . The leading causes of death in this study were cerebrovascular disease, followed by pneumonia, ischemic heart disease and cancer. The leading cause of death for women was cerebrovascular disease whilst pneumonia for men. Hemorrhagic stroke patients were more likely to die from cerebrovascular disease compared to IS patients.
In sum, older stroke patients have a higher risk of worse outcomes. Ethnic differences are seen in the outcomes of stroke depending on the type of stroke. Females have better outcomes than males only for IS patients. The stroke recorded during the subsequent hospitalization is also more likely to be of the same type as the initial stroke identified. The most common cause of death post-stroke is cerebrovascular diseases in all the stroke patients regardless the subtype of stroke.
The main strengths of this study are that we have studied about 40% of the stroke population across multi-hospitals in Singapore and have obtained complete five-year follow-up. This is the largest study of survival and recurrent stroke to date in Singapore. In addition we have used methods of survival analysis with competing risk that allowed us to estimate the risks of recurrent stroke and death simultaneously. Competing risk model is more appropriate for a condition such as stroke which is associated with a high mortality.
There are a few limitations to our study. First, we have used ICD diagnosis codes in the administrative databases to identify our study patients. Internal audit studies have shown that the coding accuracy of primary diagnoses were above 96%. However, the accuracy of coding is likely to vary with disease complexity or differ in institutions. Second, stroke patients who readmitted to other hospitals than the three study hospitals were not captured. Therefore the readmission rate due to stroke recurrence might be under-estimated in this study. However, based on internal audit studies, among all the readmitted patients in one year after discharge, less than 6% were readmitted to other hospitals. This rate may vary for patients with different diseases. Third, our risk adjustment may be inadequate because of lack of clinical details, for example the severity of stroke. Lastly, we couldn’t differentiate patients of first ever stroke or the recurrent stroke based on their index admission. The 5-year survival and recurrent rates might be very different for these two kinds of patients.