The effect of multimorbidity on sickness absence by specific diagnoses.

Background: As the world's population ages, the prevalence of multiple chronic and non-chronic health-related conditions is increasing. Research on multimorbidity, the co-occurrence of two or more health-related conditions, has mainly involved patient and older populations. Its effect in working populations, presumably younger and healthier, is not well known but could conceivably affect sickness absence (SA) and ability to return to work.

Aims: To examine the effect of multimorbidity on the incidence and duration of SA episodes by frequent diagnostic groups.

Methods: A prospective study (in 2006-2008) of workers in Spain. Information on health-related conditions was gathered with a standardized questionnaire and used to construct a sex-specific multidimensional multimorbidity score (MDMS). In order to estimate the effect of MDMS on incidence and duration of SA episodes due to cardiovascular diseases (CVD), musculoskeletal disorders (MSD) and mental health disorders (MHD), we fitted Cox models adjusted by age, occupational social class and number of prior SA episodes for both sexes.

Results: The study population was 372370. Men with high MDMS showed a trend towards higher incidence risk for SA due to CVD and MSD [adjusted hazard ratio (aHR) = 2.03; 95% confidence interval (CI) 1.48-2.78 and aHR = 1.20; 95% CI 1.01-1.43, respectively]. Women showed a similar trend for MSD, but MHD had the strongest association (aHR = 4.78; 95% CI 1.97-11.62) for high MDMS. In both sexes, the effect of MDMS was strongest among those without a prior SA. No consistent associations with SA duration were observed.

Conclusions: Multimorbidity increased the risk of incident musculoskeletal, mental and cardiovascular SA episodes but not their duration.