The effects of co-morbidity on the onset and persistence of generalized anxiety disorder in the ICPE surveys. International Consortium in Psychiatric Epidemiology.

BACKGROUND: Although it is well known that generalized anxiety disorder (GAD) is highly co-morbid with other mental disorders, little is known about the extent to which earlier disorders predict the subsequent first onset and persistence of GAD. These associations are examined in the current report using data from four community surveys in the World Health Organization (WHO) International Consortium in Psychiatric Epidemiology (ICPE).
METHOD: The surveys come from Brazil, Canada, the Netherlands and the United States. The Composite International Diagnostic Interview (CIDI) was used to assess DSM-III-R anxiety, mood and substance use disorders in these surveys. Discrete-time survival analysis was used to examine the associations of retrospectively reported earlier disorders with first onset of GAD. Logistic regression analysis was used to examine the associations of the disorders with persistence of GAD.
RESULTS: Six disorders predict first onset of GAD in all four surveys: agoraphobia, panic disorder, simple phobia, dysthymia, major depression and mania. With the exception of simple phobia, only respondents with active disorders have elevated risk of GAD. In the case of simple phobia, in comparison, respondents with a history of remitted disorder also have consistently elevated risk of GAD. Simple phobia is also the only disorder that predicts the persistence of GAD.
CONCLUSIONS: The causal processes linking temporally primary disorders to onset of GAD are likely to be state-dependent. History of simple phobia might be a GAD risk marker. Further research is needed to explore the mechanisms involved in the relationship between simple phobia and subsequent GAD.