psychotic disorders

Background: An increased prevalence of antibodies to Toxoplasma gondii has been found to be associated with psychosis. An association with positive symptom severity in a psychosis risk sample has also been reported. However, the possible association between toxoplasma and positive symptoms in the general population is unknown. Methods: We investigated whether Toxoplasma gondii is associated with psychosis diagnoses and psychotic symptoms in the general population. We used data from Health 2000, a large health survey of the Finnish population aged 30 and older (n = 5906). Levels of IgG antibodies to Toxoplasma gondii were determined and seropositivity defined as a cutoff of 50 IU/ml. Lifetime psychotic symptoms were identified with section G of the Composite International Diagnostic Interview, Munich version (M-CIDI). The CIDI screen was considered positive if the interviewee reported any clinically relevant symptom or at least 3 symptoms regardless of clinical relevance. Lifetime psychotic disorders were screened from the sample and were diagnosed with DSM-IV using case notes and SCID-I interview. The possible diagnoses were: any psychotic disorder, functional psychosis, schizophrenia, other nonaffective psychosis, and affective psychosis. Results: The seroprevalence of Toxoplasma in the population was 13%; 12% of the participants reported at least one psychotic symptom, the most common symptoms being delusions of reference and suspicion, and 4% were considered positive for the CIDI screen. In a logistic regression model, toxoplasma seropositivity was the only significant predictor of the CIDI screen status, when other variables associated with toxoplasma were adjusted for (age, gender, education, region of residence, cat ownership, and C-reactive protein measuring inflammation). Toxoplasma infection was not associated with any psychosis diagnoses. Conclusion: In a large sample representing the whole Finnish population aged 30 and older, we found that toxoplasma infection predicted psychotic symptoms but not psychosis diagnoses. The association between psychotic symptoms and toxoplasma was not explained by inflammation.