Effectiveness of a Targeted Occupational Health Intervention in Workers with High Risk of Sickness Absence: Baseline Characteristics and Adherence as Effect Modifying Factors in a Randomized Controlled Trial

Introduction In a recently published randomized controlled trial (RCT), a targeted occupational health (OH) intervention was found effective in an intention-to-treat analysis in controlling sickness absence among workers with high risk of sickness absence, compared to usual care. We performed an exploratory subgroup analysis in order to detect possible effect modifiers and mediators. Methods Age, gender, working status, severity of physical impairment, depression score, self-rated working ability, co-morbidity, and sickness absence characteristics in the previous 12 months were identified as potential effect modifiers (n = 382). We conducted regression analyses with the potential effect modifiers and a mediator (treatment attendance as intended) as explanatory variables. The difference of sickness absence days during the previous year and the follow-up year was the dependent variable. Results The intervention was especially effective in the subgroups of workers who were certain that they will not be able to continue working in their current job due to health-related reasons (−74 days; 95% CI −105 to −43), had co-morbidities (−22.5 days; 95% CI −35.5 to −9.5), or severe physical impairment at work (−17.5 days; 95% CI −28.5 to −6.5). A modifying effect of age, gender, working status, depressive symptoms, or prior sickness absence on the effectiveness of this OH intervention was not found. Conclusions This targeted OH intervention seems especially suitable for workers who consider that they are no longer able to continue working due to health reasons and have high level of physical impairment or co-morbidities. The findings from these exploratory analyses should be tested in future RCTs.