Description of Studies
The search of electronic databases yielded 4,214 articles. After reviewing the titles and abstracts, we identified 293 articles for full-article relevance screening. Following their review, 21 articles proceeded to quality appraisal. Seven additional articles were excluded at the risk of bias assessment and data extraction stages because they did not meet inclusion criteria, resulting in 14 included articles from 12 studies. Figure 1 summarises the study selection process.
Study Characteristics (See Appendix 5—Electronic Supplementary Material)
Of the studies identified, four were conducted in The Netherlands [20–24], four in the USA [25–29] and one each in Canada, Finland, Denmark, and Japan [30–34]. Ten were randomised controlled trials (RCTs) [20–29, 31–33] and two were non-randomised studies (NRSs) with a separate control group [30, 34]. Studies were conducted in a variety of settings, including workplaces [20, 29, 30, 34], primary care practices [25–28], occupational health services [21, 22, 24], and specialty medical clinics [23, 31–33].
In some studies, all participants were working at baseline [28, 29, 34], while in others, all participants were on work disability leave  or sick leave [20–22, 24]. Four studies included a mix of participants who were working, on sick leave, or unemployed [23, 25, 31–33]. One study did not report working status at baseline .
Table 3 summarises the interventions. The 12 studies identified cover a diverse range of interventions that include psychological interventions [20, 31, 32], enhanced primary care [25–28], enhanced psychiatric care , enhanced occupational physician roles [21, 22, 24], integrated care management [29, 30], exercise , and a worksite intervention .
The psychological interventions involved psychological treatments, such as cognitive behavioural therapy (CBT) and psychotherapy, which are normally delivered by psychologists or psychotherapists. However, in one trial , one of the interventions (brief CBT-based stress management with a focus on improving workplace processes) was delivered by “labour experts”. Enhanced primary care involved physicians and nurses working in the primary care centres or managed care organizations. The predominant components of this approach were education for physicians and nurses on guideline-concordant care and reinforcement to adhere to these guidelines. Enhanced psychiatric care involved out-patient psychiatric treatment enhanced by occupational therapy. Enhanced occupational physician role consisted of an intervention approach that was aimed at establishing a more active role for the occupational physician in the management of work disability and in the prevention of work disability recurrences. Systems integration and care management interventions refer to interventions conducted at the organizational or health-care system level. In this systematic review, the interventions were aimed at appropriate diagnosis, adherence to treatment, adequate follow-up, and ensuring collaboration among all individuals involved in the care management of workers with depression. The exercise intervention consisted of three different types of exercises (strength, aerobic and relaxation training) without an “inactive” control group. People with depression were referred from general practitioners, private practicing psychiatrists, psychologists or psychiatric wards to participate in exercise training twice a week for 32 weeks in a hospital setting. The worksite intervention consisted of a stress reduction program in which supervisors were asked to list possible work stressors in their worksites and to make plans to reduce these stressors while a working committee made the plans feasible. The supervisors started stress reduction activities and the committee monitored their activity periodically.
Risk of Bias in Included Studies
Overall, each study demonstrated a high risk of at least one type of bias (Table 4). All 12 studies were judged to be at an overall
high risk of bias, which reduces the certainty of the findings.
A high risk of selection bias was most common and was due to inadequate allocation methods [29, 30, 34], lack of information on allocation methods [20, 25–28], differences between participants and non-participants [25, 26, 28] and baseline differences [23, 33, 34].
Four studies demonstrated a high risk of attrition bias [27, 29, 31, 32, 34] due to important differences between those who remained in the study and those who were lost to follow-up.
Risk of performance bias was high in a number of studies due to failure to report on participants’ compliance with their assigned intervention [21, 22, 24, 29, 31, 32, 34], as well as issues of contamination [21–24, 33] and co-intervention .
Only two studies [31–33] demonstrated a high risk of measurement bias owing to the lack of blinded outcome assessment.
Reporting bias was high in three studies [25–27, 29] due to the use of multiple imputations for large quantities of missing data.
As all of the studies were judged to have high risk of bias and many outcomes—based on evidence from only one study—lacked precision and consistency, the grade of evidence in all cases was considered to be “very low”.
Half of the studies assessed the impact of an enhanced physician role. However, the type of enhancements and quality improvements were very different and varied according to the distinct disability insurance and health care system in place. Primary care enhancements were conducted in the USA [25–28] and included education on guideline-concordant interventions, screening for depression, and more frequent contacts with patients especially regarding adherence to treatments (pharmacological or psychotherapy). The results from these studies were mixed (positive and neutral). In another study , psychiatric care was enhanced by the addition of an occupational therapist that focused on contacting the worker and the employer to discuss a program for work reintegration. This study was conducted in The Netherlands and the results were mixed (positive and neutral). An enhanced occupational physician role was examined in two studies from The Netherlands [21, 22, 24] where they evaluated a more active role for the physician by guideline-based education and facilitation of RTW. The results were mixed (positive and neutral).
The studies examining integrated care management showed mixed findings (positive and neutral) [29, 30] and one study of a psychological intervention that used an inactive control  showed mixed findings (positive and neutral, and negative and neutral). One study of a worksite stress reduction program was conducted in Japan and showed positive findings . One trial of exercise did not have an inactive control group .
Because the evidence was graded as “very low” for all outcomes identified, the key message from this review is that some intervention approaches are feasible and could therefore be further evaluated in future studies:
Enhanced Primary Care
Enhanced Psychiatric Care
Enhanced Role for the Occupational Physician
Worksite Stress Reduction
Integrated Care Management