Cohort approach in tuberculosis surveillance: comparison of the situation in Sweden and Finland

Finland and Sweden.

To present and compare the long-term trends of the tuberculosis situation and especially the experiences of different birth-year cohorts.

Analysis of morbidity and mortality statistics since the early 1950s. The grouped birth-year cohorts are followed at 5-year intervals.

In both countries the morbidity and mortality rates have diminished in a similar fashion. The Finnish situation follows the Swedish one by a delay of about 15 years. The incidences in the younger age groups have diminished markedly, but in the older ones the progress has been much less rapid. The median age of new cases has increased continuously. In Sweden, obviously due to the great number of immigrants, this trend has ceased in recent years. In each cohort born this century, the highest morbidity rates have been experienced at the age of around 20-30 years. After this they diminish exponentially at about the same speed, at least in recent times.

The high prevalence of tuberculosis infection reached in early life seems to introduce a high lifelong incidence of the disease. In the older age cohorts the relatively high rates at present still reflect the circumstances in the 1940s or earlier. Age-oriented long-term surveillance can give useful information on the dynamics of the tuberculosis epidemic.