Study of a cohort of patients newly diagnosed with depression in general practice: prevalence, incidence, comorbidity, and treatment patterns.

Objective: To estimate the prevalence and incidence of depression; investigate its association with risk factors including comorbidities and drug and health care use; and describe treatment patterns of depression in primary care using The Health Improvement Network database.

Method: In this cohort study, subjects with a first recorded diagnosis of depression (Read code) between January 1, 2002, and December 31, 2004 (n=47,170) were identified from a source population of 1,287,829 subjects aged 10-79 years. A comparison group was sampled from the same population and frequency matched to the depression cohort by age, sex, and calendar year (n=50,000). Depression diagnoses were validated using physician-completed questionnaires. Odds ratios and 95% CIs for the relationship of depression with a range of factors were estimated using unconditional logistic regression in a nested case-control analysis.

Results: The prevalence of depression was 11.23% (95% CI, 11.18-11.28). This prevalence decreased with increasing age and was higher in women than in men. The incidence was 13.89 per 1,000 person-years (95% CI, 13.82-14.08). Depression was associated with frequent use of health services, smoking, pregnancy in the previous year, anxiety, stress, sleep disorders, digestive and respiratory disorders, and pain. In the trimester following diagnosis, 82% of cases were treated-98% with antidepressants and 81.5% with selective serotonin reuptake inhibitors (SSRIs).

Conclusions: We found a high prevalence and incidence of depression diagnoses in primary care in the United Kingdom. Following diagnosis, the majority of individuals were prescribed SSRIs. A diagnosis of depression is associated with a number of prior comorbidities, which could mask the depression. This fact should be taken into account when screening individuals in primary care.