Epidemiology of depression in primary care.

Major depressive disorder has been recently found to be associated with high medical utilization and more functional impairment than most chronic medical illnesses. Major depression is a common illness among persons in the community, in ambulatory medical clinics, and in inpatient medical care. Studies have estimated that major depression occurs in 2%-4% of persons in the community, in 5%-10% of primary care patients, and 10%-14% of medical inpatients. In each setting there are two to three times as many persons with depressive symptoms that fall short of major depression criteria. Recent studies have found that in one-third to one-half of patients with major depression, the symptoms persist over a 6-month to one-year period. The majority of longitudinal studies have determined that severity of initial depressive symptoms and the presence of a comorbid medical illness were predictors of persistence of depression.