Tuberculin status, socioeconomic differences and differences in all-cause mortality: experience from Norwegian cohorts born 1910-49.

BACKGROUND

From 1948 to 1975, Norway had a mandatory tuberculosis (TB) screening programme with Pirquet testing, X-ray examinations and BCG vaccination. Electronic data registration in 1963-75 enabled the current study aimed at revealing (i) the relations between socioeconomic factors and tuberculosis infection and (ii) differences in later all-cause mortality according to TB infection status.

METHODS

TB screening data were linked to information from the Norwegian Cause of Death Registry (1975-98) and the National Population and Housing Censuses (1960, 1970 and 1980). Analyses were done for 10 years cohorts born 1910-49, separately for men (approximately 534,000 individuals) and women (608,000), using logistic and Cox regressions.

RESULTS

TB infection and X-ray data confirmed the strong regional pattern seen for TB mortality, with the highest rates in the three northernmost counties and higher rates in urban than rural areas. High socioeconomic status relates to lower odds both for TB infection and TB-related chest X-ray findings (odds ratios 0.6-0.7 for highest vs lowest educational groups). Those infected by TB, and especially those with chest X-ray findings, have increased all-cause mortality in at least a 20 years period following determination of tuberculin status (hazard ratios approximately 1.15 and 1.30, respectively, higher for late than early cohorts).

CONCLUSIONS

TB particularly affected lower socioeconomic strata, but even those in higher strata were at high risk. The differences in all-cause mortality could partly be attributed to socioeconomic factors, but we hypothesize that developing TB infection may also indicate biological frailness.