Major depression is highly prevalent, often chronic or recurrent, and among the most disabling and costly of illnesses, yet its burden is often unrecognised. Historically, the primary care sector of the US health system has played a large role in both the mental and physical healthcare of patients with depression (Regier et al, 1993; Kessler et al, 2003). This role is amplified by the managed care industry, which may emphasise restricted access to specialty care in its efforts to limit costs. This chapter reviews state-of-the-art research on the treatment of depression in primary care, with special attention to the measurement tools used to support outcomes assessment.

Epidemiology, service use and costs of depression in primary care

Prevalence of disorder

In the general population, the 12-month prevalence of major depressive disorder has been estimated at 6.6%, according to the US National Comorbidity Survey Replication (NCS-R; Kessler et al, 2003). About a quarter to a half of patients with depression are treated in primary care (Narrow et al, 1993; Regier et al, 1993; Kessler et al, 2003) and, accordingly, the disorder is highly prevalent in primary care, with a point prevalence estimated at 5–10% (Katon et al, 1992, Simon & Von Korff, 1995) among adults 18 years of age and older.

Disability

According to the World Health Organization Global Burden of Disease Study, unipolar major depressive disorder was the fourth leading cause of worldwide disability for both sexes in the 1990s (Murray & Lopez, 1996a). It is projected that depression will rank as the second largest contributor to the worldwide burden of disease by 2020 (Murray & Lopez, 1996b). The Medical Outcomes Study (MOS) demonstrated that physical functioning and well-being scores on the 36-item Short Form (SF–36) for patients with major depression were comparable, and in some cases significantly worse than scores for patients with other chronic medical conditions. Mental functioning and well-being scores were consistently and significantly worse for the MOS patients with depression than for patients with medical illnesses (Hays et al, 1995). Another longitudinal observational study compared primary care patients with depression during their ‘worst-functioning’ assessment interval with participants who did not have depression (Rost et al, 1998).