Seroepidemiology of Toxoplasma gondii Infection in Psychiatric Inpatients and Healthy Controls in North Iran: A Case-Control Study.

OBJECTIVE

Gorgan, in northern Iran, is a humid region where Toxoplasma gondii is common. The association with psychiatric illness has never been examined there. We measured seroprevalence in psychiatric inpatients and matched controls, quantified it for each major DSM-5 diagnostic category, and identified local risk factors for infection.

METHOD: A case-control study was conducted with 100 psychiatric inpatients and 100 healthy controls, frequency-matched 1:1 on sex and 5-year age stratum. Diagnoses were recorded as free text at discharge by the attending psychiatrists under DSM-5 criteria and were mapped to six categories using rules fixed in advance. Sera were tested for anti-T. gondii IgG and IgM by ELISA. Associations were estimated by logistic regression, with secondary analyses comparing each diagnostic category with the controls.

RESULTS

Anti-T. gondii IgG seroprevalence was 39.0% in patients and 47.0% in controls (OR = 0.721, 95% CI: 0.411-1.265, p = 0.254; adjusted for the matching variables, OR = 0.668, 95% CI: 0.359-1.240, p = 0.201); IgM positivity was rare (1.0% vs. 0%). No diagnostic category differed from controls. Seroprevalence was 38.9% in schizophrenia spectrum and other psychotic disorders (n = 18; OR = 0.73), 34.8% in bipolar and related disorders (n = 23; OR = 0.62), 36.4% in depressive disorders (n = 22; OR = 0.66), and 57.9% in substance- or medication-induced disorders (n = 19; OR = 1.52). Heterogeneity across categories was not significant (p = 0.533). Psychiatric status did not predict seropositivity (aOR = 0.85, 95% CI: 0.42-1.70). Age was the only consistent independent predictor (aOR = 1.08 per year, 95% CI: 1.04-1.11, p < 0.001), seroprevalence rising from 5.0% at 20 years or younger to 72.2% above age 50.

CONCLUSION

Latent toxoplasmosis was not associated with psychiatric disorder overall or within any diagnostic category. Seroprevalence was governed principally by cumulative age-related exposure. These data add to a growing set of null and inverse reports from high-endemicity settings and indicate that the epidemiological expression of this association is context-dependent.