Study characteristics and the selection process
Overall, 8408 records were generated from four electronic databases including PubMed (1654), Scopus (2857), Google scholar (3670) and Embase databases (227), respectively. No grey literature was included. The preliminary screening based on titles and abstracts identified forty-one papers as potentially relevant for the full-text review and thirty two articles were finally deemed eligible for the systematic review and meta-analysis (fig 1).
Thirty two studies assessed overall mortality due to stroke. Twelve studies were from Africa [7-8, 17-26], six from Europe [27-32], six from Asia [33-38], five from North America [39-43] and two from Latin America [44-45].Seventeen studies reported 30-day mortality rate of stroke whereas twenty two studies measured in-hospital mortality. Detailed explanations on study characteristics are shown in the supplementary table (table 1).
Patient Characteristics
A total number of 2,885, 126 patients were recruited for the study. The mean age of participants was found to be 69.8± 13.8 years. There were 1172581(40.64%) males and 1712545(59.36%) females, respectively. Overall stroke mortality was documented for 302,592 (10.49%) patients. The rate of 30-day mortality was reported in 19057(0.66%) subjects while in-hospital mortality was recorded in 108, 368 (3.75%) participants.
Types of stroke
About 121 3064 (42%) patients experienced ischemic stroke. hemorrhagic stroke was identified in 190,906(6.6%) of patients. The remaining stroke events were undifferentiated or unclassified.
Risk factors
The following risk factors were reported hypertension 1159461(40.2%) with mean systolic blood pressure of 154.29±21.45 mmHg, diabetes 195612 (6.78), AF: 216097 (7.49%), hypercholesterolemia: 420144 (14.5%), alcohol consumption: 30902 (1.71%), smoking: 163583 (5.67%), cardiomyopathy 3987(0.14%) and previous stroke attack 39833(1.4%). The risk factors for rest of the population were not distinguished.
Complications of stroke
Complications were reported in 10,622subjects. Specific complications include confusion 4629(43.57%), thromboembolism 170(1.6%), mobility disorder 1573(14.81%), speech disorder 1550(14.59%), infection 465(4.38%), cognitive problem 731(6.9%), neurologic complications 1504(14.16%).
Mortality of stroke
Pooled estimate indicated that the overall mortality of stroke was reported to be 20% (19%-22%). Whereas, the 30-day mortality was found to be 18% (16%-20%). In-hospital mortality was estimated as 16% (16%-19%) (Fig 2-4).
Subgroup analysis
To examine the difference in the epidemiology of stroke mortality among continents and type of study designs, a subgroup analysis was undertaken based on the location of the studies and study designs. Consequently, It was found that Africa registered the highest stroke-related death 29% (23%-36%) followed by Europe 22% (16%-27%). (Fig. 5) America, 16% (12%-20%) and Asia 16% (10%-21%) showed a comparable rate of overall stroke mortality (Figure 5).Mortality was higher among prospective studies 26% (22%-31%) versus retrospective 17% (15%-20%) (Additional file 1).
Determinants of mortality
Pooled odds ratio of precipitating factors revealed that hypertension was found to be an important risk factor for mortality secondary to stroke 61.9% (52.8%-71.1%). The probability of death has increased in a quarter among stroke patients who were having hypercholesterolemia 20.2% (10.0%-30.4%) and alcohol consumption 21.5% (10.4%-32.6%), respectively (table 2).
Sensitivity and subgroup analysis
The sensitivity analysis showed that omission of anyone of the included studies did not significantly affect the pooled mortality of stroke (all P < 0.05) (additional file 2). We performed subgroup analysis based on geographic area of the studies and the type of study design. Accordingly, overall mortality was found to be higher in Africa 29% (23%-36%) than any other continents (fig 5).In addition, mortality was higher among prospective studies 26% (22%-31%) versus retrospective 17% (15%-20%) (Additional file 3).