Stroke case fatality in Denmark from 1977 to 1992: the Copenhagen City Heart Study

Stroke mortality rates have decreased in Denmark but little is known about the reasons for these changes. One possible explanation is decreased case-fatality, and the aim of the present investigation was to study trends in case-fatality for first-ever stroke in a large population-based cohort study in Copenhagen, Denmark.

The Copenhagen City Heart Study comprised 19,698 inhabitants in Copenhagen, Denmark. Linkage to two national registers enabled identification of all subjects irrespective of participation in the study examinations. Follow-up in the present study was from January 1, 1977 to December 31, 1992. Case fatality after 7 days, 28 days, 1 year and 1 year in 28-day survivors was assessed for first-ever stroke. Uniform identification and validation methods made it possible to estimate trends in case-fatality. The World Health Organization's definition of stroke was used, and stroke was categorized into either unspecified stroke, ischemic infarction, intracerebral hemorrhage, or subarachnoid hemorrhage. The effect of time was estimated by means of multiple logistic regression analyses adjusting for gender, age at onset and type of stroke.

A total of 1,213 strokes occurred during the study period from 1977 to 1992 in the study population. The case-fatality was highest during the first 28 days, and especially the initial 7 days; thereafter a steady state was reached. From the period 1977-1980 to the period 1989-1992 case-fatality did not change in analyses of 7-day case-fatality odds ratio (OR) = 1.14 (95% confidence interval, CI: 0.98-1.33), or of 28-day case-fatality OR = 1.06 (95% CI: 0.92-1.20), or of 1-year case-fatality OR = 0.95 (95% CI: 0.84-1.07). In the 1-year case-fatality, including only 28-day survivors, a significant decrease was found OR = 0.81 (95% CI: 0.67-0.97). Men had a significantly lower 7-day case-fatality than women; OR = 0.73 (95% CI: 0.52-0.99), but the difference attenuated in subsequent analyses and did not remain statistically significant.

During the period 1977-1992, the 1-year case-fatality decreased in stroke patients who survived the initial 28 days, whereas no changes were observed in 7-day, 28-day and 1-year case-fatality.