Are changes in mortality from stroke caused by changes in stroke event rates or case fatality? Results from the WHO MONICA Project.

BACKGROUND AND PURPOSE Mortality from stroke has been declining over recent decades in most countries, except in Eastern Europe. In this analysis, based on the World Health Organization Monitoring Trends and Determinants in Cardiovascular Disease (WHO MONICA) Project, we explored to what extent these trends are due to changes in stroke event rate and to changes in case fatality. METHODS The WHO MONICA Project collected standardized data from 14 populations in 9 countries. All acute strokes occurring in men and women 35 to 64 years of age were included. Registration was carried out between 1982 and 1995, resulting in time spans from 7 to 13 years. Trends in event rates and case fatality were calculated as average annual percentage change. RESULTS Up to 6-fold differences were observed in stroke mortality. Mortality declined in 8 of 14 populations in men and in 10 of 14 populations in women. An increase in mortality was observed in Eastern Europe. In the populations with a declining trend, about two thirds of the change could be attributed to a decline in case fatality. In populations with increasing mortality, the rise was explained by an increase in case fatality. CONCLUSIONS In most populations, changes in stroke mortality, whether declining or increasing, were principally attributable to changes in case fatality rather than changes in event rates. Whether this was due to changes in the management of stroke or changes in disease severity cannot be established on the basis of these results.