Lifetime and 12-month prevalence rates of sub-clinical psychosis symptoms in a community cohort of 50-year-old individuals

Background: Estimation of prevalence rates of sub-clinical psychosis symptoms can vary considerably depending on the methodology used. Furthermore, discussions are ongoing how prevalence rates may differ across various syndromes. Method: We analyzed data from the prospective Zurich Study, assessing sub-clinical psychosis with a semi-structured clinical interview in a community cohort of 50 years old individuals. The higher-order factors of psychosis symptoms were analyzed with confirmatory factor analysis to validate the a priori specified symptom-structure. Further associations were examined with contingency tables and logistic regressions. Results: The confirmatory factor analysis was consistent with a structure with four higher-order syndromes. Those different syndromes were labeled "thought disorder" (lifetime prevalence = 10.6%), "ego disorder" (4.8%), "hallucination" (9.7%), and "schizotypy" (28.2%). A strong discrepancy was noted between the 12-month prevalence of any symptoms and those considered to be severe. Twelve-month prevalence rates of distressful syndromes ranged from 0.1% for hallucinations up to 6.6% for schizotypy. The most strongly interrelated syndromes were thought disorder and ego disorder (OR = 12.4). Conclusion: Our findings indicate a continuity of sub-clinical psychosis within the general population even though only a small proportion suffers from distressing symptoms. Our analyses showed that the syndromes identified here are similar to those found in full-blown schizophrenia, albeit in an attenuated form. (C) 2012 Elsevier Masson SAS. All rights reserved.