Prevalence and correlates of psychotic-like experiences in the Australian community

Background: Apart from individuals with clinical psychosis, community surveys have shown that many otherwise-well individuals endorse items designed to identify psychosis. The clinical relevance of psychotic-like experiences (PLE) in individuals who are not psychotic is not clear. This thesis aimed to examine the prevalence, demographic and psychosocial correlates and antecedents of PLE in the Australian community. Method: Data from three population-based studies was examined. The Australian National Survey of Mental Health and Wellbeing interviewed 10,641 individuals living in private dwellings in Australia. We examined the impact of selected demographic variables on endorsement of psychosis screen and probe items from the Composite International Diagnostic Interview (CIDI). We also examined the effect of exposure to traumatic events (with and without Post Traumatic Stress Disorder (PTSD)) on the endorsement of CIDI psychosis items. The youth component of the Australian National Survey of Mental Health and Wellbeing collected demographic and clinical data on a nationally representative sample of 1261 adolescents aged 13-17 years. The prevalence of hallucination endorsement on the Youth Self Report (YSR) in Australian adolescents was examined. The association between hallucination endorsement, demographic variables (sex, age, urbanicity and family composition) and clinical variables (self-reported depression, marijuana and alcohol use, DSM IV diagnoses, emotional/ behavioral problems as reported by the parent on the Child Behaviour Check List (CBCL)) were examined. The Mater- University of Queensland Study of Pregnancy (MUSP) is a prospective longitudinal birth cohort study of 7223 mothers and their offspring who received antenatal care between 1981 and 1984. Psychotic-like experiences were assessed in the offspring at the 21 year follow-up using the Peters Delusional Inventory (PDI) and the CIDI. We examined the prevalence of PLEs, and examined the effect of age (the age range at the 21 year follow-up was 18 to 23 years) and sex on PLE. A second study examined the emotional and behavioural antecedents of PLE at 21 years as measured by the CBCL at five and 14 years and the YSR at 14 years. Results: An estimated 11.7% of Australian adults endorsed at least one psychosisscreening item. Higher endorsement was associated with younger age, migrants from non- English speaking backgrounds, not being married, unemployment, living in an urban region and lowest socioeconomic levels. Exposure to any traumatic event was associated with increased endorsement of PLE (Rate Ratio =2.68; 95% CI 2.18, 3.30). A diagnosis of PTSD further increased endorsement of PLE (Rate Ratio =9.24; 95% CI 6.95, 12.27). Hallucinations were reported by 8.4% of Australian adolescents. Those living in blended or sole parent families were more likely to report hallucinations than those living with both biological parents (OR 3.27; 95% CI 1.93, 5.54; OR 2.60; 95% CI 1.63, 4.13 respectively). Hallucinations were more prevalent in adolescents who had high CBCL scores or elevated depression symptoms (OR 3.30; 95% CI 2.10, 5.20; OR 5.02; 95% CI 3.38, 7.45 respectively). Hallucinations were more prevalent in those adolescents who had smoked cannabis more than twice in the month prior to the survey (OR 3.27; 95% CI 1.76, 6.08). In the 21 year follow-up of the MUSP study, older age (18-20 compared to 21-23 years) was significantly associated with a reduction of CIDI delusions (OR 0.66, 95% CI 0.48, 0.92) and PDI total scores (OR=0.68, 95% CI 0.55, 0.83). Women were significantly more likely to endorse items related to hallucinations (OR=1.49, 95% CI 1.14, 1.95) but not delusions. High CBCL scores at 5 and 14 years predicted high total PDI scores; Those in the highest quartile of YSR scores at 14 years were nearly four times more likely to have high levels of psychotic-like experiences at age 21 (OR=3.71, 95% CI 2.92, 4.71). Adolescent onset psychopathology and continuous psychopathology through both childhood and adolescence strongly predict PLE at age 21. Conclusions: Psychotic-like experiences are relatively common in population surveys of Australian adults and adolescents. In adults, the demographic correlates of PLE are similar to those of schizophrenia. There is a strong association between PLE and exposure to trauma. The correlates of PLE in adolescents are different to those of adults. The reduction in prevalence of delusions between late adolescence and young adulthood is coincident with normal neurophysiological changes in the frontal lobes, suggesting hypotheses suitable for future research. The association between marijuana use and hallucinations in adolescents is further evidence of the potential harm caused by use of cannabis. The onset or persistence of emotional distress during adolescence is associated with an increased risk of PLE in adulthood. These findings are relevant to both clinical practice and future research. Psychotic symptoms create diagnostic uncertainty. There is potential for patients with anxiety (PTSD) or mood disorders to be incorrectly diagnosed with a psychotic illness and receive inappropriate management. Equally, there is a risk that subjects who have an emerging psychotic disorder and comorbid anxiety or depression or have had exposure to traumatic events may have treatment of their psychosis delayed as psychotic symptoms are incorrectly ascribed to a syndrome other than psychosis. Clinicians need to be aware of this diagnostic tension so that accurate assessments and appropriate treatments can be initiated at the earliest possible opportunity. The resolution of childhood emotional distress prior to adolescence appears to reduce the risk of PLE and possibly psychosis in adults. Strategies targeting emotionally distressed children may offer opportunities for psychosis prevention. Further research is required to explore the relationship between PLE and vulnerability to psychosis and other mental health problems. It remains unclear if PLE are reliable endophenotypes for schizophrenia. If this is the case, examining genetic and environmental risk factors for onset and persistence of PLE, and the neuroimaging changes that occur as individuals with PLE convert to psychosis will provide important new clues to our understanding of the aetiopathogenesis of psychosis