Estimating incidence and prevalence from population registers: example from myocardial infarction

Aim: To illustrate how the fundamental epidemiological measures, incidence rate and prevalence proportion, can be estimated based on Swedish population registers using acute myocardial infarction (MI) as an example, together with a discussion about the analytical decisions. Methods: All individuals in Sweden aged 60–89 (born 1904–1954) during the study period 1994–2014 were identified through the Total Population Register. Cases of MI were defined and identified from information on hospital admissions and causes of death. Incidence rates of all, first, and recurrent MI were calculated together with prevalence proportions. Results: The incidence rate of all, first, and recurrent MI declined over the study period. While the incidence rates of first MI are lower for women than men, the incidence rates of recurrent MI are considerably higher but similar for men and women. The prevalence calculated with duration of disease set at 28 days also declined. This was despite improved survival from MI and increased life expectancy over the same period meaning that the decline in incidence was large enough to compensate for increased survival. Conclusions: Calculating incidence and prevalence of diseases using population registers requires detailed and well-reasoned definitions. The definitions will affect both the study population and the number of disease events and it is essential that the cases and the study population are defined in a coherent way. Different measures of disease occurrence contribute with different aspects of the disease panorama and a joint interpretation contributes to a thorough understanding of the disease development in a population.