As part of the DETECT study, a nationwide representative clinical-epidemiological study, the frequency and associated problems of comorbid depression with a wide range of somatic illnesses were studied in N = 51,000 primary care patients. Further the association with health related quality of life and disability is examined. Depression was assessed with the Depression Screening Questionnaire (DSQ) with an ICD-10 algorithm.
Results: (1) 7.5 % of all primary care patients met criteria for ICD-10 depressive disorders. (2) Depression risk was increased whenever any somatic disorder was present and increased in a dose-response relationship by number of comorbid conditions. (3) Elevation of depression risk was fairly independent of type of diagnosis, although associations with coronary heart disease (OR: 1.7), diabetic complications (OR: 1.7- 2.0), stroke (OR: 2.5) and pain-related chronic disorders (OR: 1.5) were particularly pronounced. Moderate associations were found for hyperlipidaemia (OR: 1.1). (4) Associated with the increasing number of comorbid conditions, patients with comorbid depression had increasingly more disability days and lower health related quality of life. It is concluded that the degree to which the frequency and the deleterious effects of comorbid depression is underestimated and unrecognized is alarming. The use of comorbidity indices might improve recognition.