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

Abstract

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