Trends in Stroke Incidence in High-Income Countries in the 21st Century

Population-Based Study and Systematic Review

Linxin Li, DPhil; Catherine A. Scott, BMBCh; Peter M. Rothwell, FMedSci

Disclosures

Stroke. 2020;51(5):1372-1380. 

In This Article

Discussion

In this updated systematic review of all population-based stroke incidence studies in high-income countries, we showed that the previously suggested 1.1% yearly percentage reduction in stroke incidence from the 1970s to early 2000s[2] is maintained and stroke incidence continued to decline at an annual rate of 1.0% to 1.5% in the last 3 decades. However, with the aging population, even if the age-specific stroke incidence continued to decrease at its current rate, there would still be a 13% increase of the number of first-ever strokes in the United Kingdom in year 2045.

Our findings based on population-based stroke incidence studies in high-income countries are supported by data from hospital-based registries, which also show a steady decline of hospitalized stroke in recent years in southeast Asia,[34] Western Europe,[35–37] and North America.[38–40] The results are also consistent with the data modeling results from the Global Burden of Disease analysis.[5] Moreover, it is encouraging that the previously suggested 1.1% yearly percentage reduction in stroke incidence from the 1970s to early 2000s was maintained,[2] possibly due to continued effort in implementing preventive treatment at the population level to reduce smoking, hypertension, and other vascular risk factors.[19,36,41,42]

However, even if stroke incidence continued to decline at its current rate, there would still be a 13% increase of the number of new strokes in the United Kingdom in year 2045 due to the aging population. Similar projections have also been reported for other European countries.[27,32,33] Moreover, reduced stroke case fatality in high-income countries would lead to growing numbers of stroke survivors, contributing to the increase of the overall burden of stroke.[10]

There was variation in the annual reduction rates between studies, with Dijon[16] showing the least steep slope and Örebro,[18] Martinique,[15] and Porto[13] showing the most prominent reduction. In other studies based on administrative data, one Swedish study and 2 Japanese registries also reported less marked reduction rates in the early 2000s than those from other high-income countries.[6,7,43] The overall difference in the time trends may reflect the difference by stroke subtypes between studies. While some studies found consistent decline for all types of strokes,[13,15] others reported diverging trend for ischemic stroke versus hemorrhagic stroke.[12,17,19,4–46] Moreover, although consistent decline for men and women was found in our pooled analysis and also reported in other hospital-based registries,[39] the Erlangen study only found a significant decline for men.[14] Given that the included population-based studies had broadly similar ascertainment methods and also maintained consistent methodology over time, the observed differences between studies would appear to be real and may be accounted for by differences in life expectancy, risk factor prevalence, control of risk factors, and accessibility of health services.[30]

Notably, in contrast to a steady decline of stroke incidence for ischemic stroke, our estimate suggested less marked change of stroke incidence for intracerebral hemorrhage in more recent years. This apparent divergent trend could perhaps be explained by increasing use of antithrombotic treatment at older ages, especially with the increasing burden of atrial fibrillation.[44]

Both OXVASC and the Porto stroke registry[13] found no significant reduction in nondisabling stroke in the past 10 years. Cerebrovascular events could have become less severe due to implementation of preventive treatment or less disabling due to improved acute stroke care. On the other hand, increasing public awareness of stroke symptoms and growing use of neuroimaging and diagnostic awareness among healthcare providers might have also resulted in improving ascertainment of minor strokes over time.

Although we consider our findings to be valid, our study has limitations. First, although we confined our analysis to high-quality population-based stroke incidence studies that maintained the ideal methodology over time, completeness of ascertainment might have changed over time.[47] However, we found a consistent and steady decline across all studies. Second, we only had aggregated data from published results and were, therefore, unable to assess thoroughly potential reasons for the observed overall temporal trends or the heterogeneity between studies, particularly if any demographic change, such as change in occupation or standard of living, had any role in explaining the observed trends across studies. Third, proportion of unclassified stroke differed considerably between studies, with further variation over time. Therefore, it was difficult to provide accurate pooled estimates comparing the temporal change of incidence in ischemic versus hemorrhagic strokes. Moreover, most studies did not provide data on the change of etiological subtypes of ischemic strokes over time. We were also unable to compare the incidence change by stroke etiology. However, one recent systematic review of population- and hospital-based studies suggested an increasing trend of cardioembolic stroke and a decrease for lacunar stroke in high-income countries in the last 30 years.[48]

In conclusion, stroke incidence is continuing to decline in Oxfordshire and in other high-income settings in the last 30 years. However, with the aging population, even if the age-specific stroke incidence continued to decrease at its current rate, the number of new stroke cases annually in high-income countries would continue to increase in the next 30 years.

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