Seasonality in affective disorders in Switzerland.

Objective: To estimate the prevalence of seasonal affective disorder (SAD) and its subsyndromal form (S-SAD) in Switzerland (47 degrees N).

Method: A representative sample from all three language areas of Switzerland (n = 980) were given a structured telephone interview using the extended Seasonal Pattern Assessment Questionnaire (SPAQ+). A smaller, but also representative sample in the city of Basel filled in the SPAQ+ form as well as undergoing a structured diagnostic interview.

Results: In this Swiss sample, 2.2% of the population presented with symptom severity of SAD, 8.9% with S-SAD. In Basel, a much higher prevalence of SAD was found. Seasonal problems occurred more often in patients with the Diagnostic and Statistical Manual (DSM)-III diagnosis of major affective disorders than in those with pure anxiety disorders or no psychiatric diagnosis.

Conclusion: These estimates for SAD in Switzerland are similar to those found in the Zürich Study, using other methods, and for populations in the UK, with the limitations inherent in retrospective questionnaire studies.