Incidence and outcomes for stroke in Ulaanbaatar, Mongolia, during 2019-21: a prospective population-based study

Background: In the absence of reliable data to quantify the burden of stroke, we aimed to determine the incidence and outcome of stroke through the conduct of a prospective population-based study in Ulaanbaatar, Mongolia, during 2019-21.

Methods: All cases of stroke were identified through surveillance of multiple overlapping sources of hospitalised, ambulatory, and deceased individuals, using standardised diagnostic criteria in adult (aged ≥16 years) residents of the six urban districts of Ulaanbaatar, Mongolia (population person-years, N=1 896 965) between Jan 1, 2019, and Dec 31, 2020. Data on sociodemography, medical history, and management were collected. Crude and standardised incidence were calculated for first-ever stroke and its major pathological subtypes, and reported with 95% CIs. Outcomes were 28-day case fatality ratios and functional recovery on the modified Rankin scale at 90 days and 1 year.

Findings: 3803 strokes in 3738 patients were identified, of which 2962 were first-ever incident cases (mean age 59 years [SD 13], 1161 [39·2%] females). Annual incidence of first-ever stroke (per 100 000) was 156·1 (95% CI 150·5-161·8) on a crude basis, 171·6 (157·5-185·6) when age-adjusted to the Mongolian population, and 140·3 (136·7-143·9) when age-adjusted to the world population. World-adjusted incidence of pathological subtypes were 66·6 (95% CI 64·8-68·3) for ischaemic stroke, 54·5 (53·0-56·1) for intracerebral haemorrhage, and 18·7 (18·3-19·1) for subarachnoid haemorrhage. Men were twice as likely to suffer ischaemic stroke and intracerebral haemorrhage as women, but the risks were similar for subarachnoid haemorrhage; these patterns were consistent across age-groups. The predominant risk factors were hypertension seen in 1363 (63·1%) of 2161, smoking in 596 (26·8%) of 2220, regular alcohol consumption in 533 (24·0%) of 2220, obesity in 342 (16·1%) of 2125, and diabetes in 282 (12·7%) of 2220. There was little use (0·9%) of thrombolysis for acute ischaemic stroke, partly due to delays in presentation after the onset of symptoms (median 16·0 h [IQR 3·0-48·0]). The 28-day case-fatality rate was 36·1% (95% CI 34·3-37·9) overall, and 14·8% (12·8-16·7) for ischaemic stroke, 52·9% (49·9-55·8) for intracerebral haemorrhage, and 54·3% (49·4-59·1) for subarachnoid haemorrhage. Corresponding figures for poor functional outcome at 1-year, defined by scores of 3-6 for death or dependency on the mRS, were 61·6% (95% CI 59·8-63·4), 47·5% (44·7-50·3), 77·0% (74·5-79·5), and 61·8% (57·0-66·5), respectively.

Interpretation: The urban population of Ulaanbaatar, Mongolia, has a high incidence of stroke, particularly for intracerebral haemorrhage and subarachnoid haemorrhage, from which half of patients die within 1 month and more than two-thirds are either dead or dependent at 90 days. Although the overall incidence of stroke is similar to other countries, it occurs at a mean age of 60 years, which is at least 10 years younger than in high-income countries. These epidemiological data can inform the implementation of future programmes and scale-up activities for the primary and secondary prevention of stroke, and in the organisation of systems of care.

Funding: Science and Technology Foundation of the Ministry of Education, Culture, and Science of Mongolia and The George Institute for Global Health.