Long-term sickness absence of 32 chronic conditions: a Danish register-based longitudinal study with up to 17 years of follow-up

OBJECTIVES: Sickness absence has been used as a central indicator of work disability, but has mainly been examined in single diseases, with limited follow-up time. This study identified the risk of long-term sickness absence (LTSA) of 32 chronic disease groups in the first year after diagnosis and the subsequent years. SETTING: We identified chronic disease groups prevalent in the work force (26 physical and 6 mental conditions) requiring all levels of care (primary, secondary, tertiary), by national registers of diagnoses from all hospital visits and prescribed medicine in Denmark from 1994 to 2011. PARTICIPANTS: A general population sample within the working age range (18–59 years) was drawn by Statistics Denmark. Participants not working before and during the follow-up period were excluded. A total of 102 746 participants were included. PRIMARY AND SECONDARY OUTCOME MEASURES: HRs of transitions from work to LTSA of each of the chronic conditions were estimated in Cox proportional hazards models for repeated events—distinguishing between risk within the first (<1 year) and subsequent years of diagnosis (≥1 year) and an HR ratio (HRR): HR ≥1 year divided by HR <1 year. RESULTS: Almost all the conditions were associated with significantly increased risks of LTSA over time. The risks were generally more increased in men than in women. Three main patterns of LTSA were identified across diseases: strong decreases of LTSA from the first to subsequent years (eg, stroke in men <1 year: HR=7.55, 95% CI 6.45 to 8.85; ≥1 year HR=1.43, 95% CI 1.20 to 1.74; HRR=0.23). Moderate or small decreases in LTSA (HRR between 0.46 and 0.76). No changes (HRR between 0.92 and 0.95) or increases in elevated risks of LTSA over time (HRR between 1.02 and 1.16). CONCLUSIONS: The 32 chronic diseases were associated with three different risk patterns of LTSA over time. These patterns implicate different strategies for managing work disability over time.