Previous studies suggested that patients with schizophrenia had an increased prevalence of antibodies against toxoplasma gondii (TG) and that those seropositive patients had higher symptom severity. However, there is no data on the relationship between treatment-resistant schizophrenia (TRS) and TG seroprevalence.

To determine the association between TRS and TG seropositivity, and to further investigate the relationship between TG seropositivity and different clinical features of schizophrenia.

In this cross-sectional study, we included 210 male inpatients with schizophrenia. TG seropositivity was determined by ELFA assay. Treatment-resistance was defined as a failure of at least 2 adequate anti-psychotic trials. Data were analyzed using χ² test or Mann–Whitney test.

The rate of TG seropositivity in the entire sample was 52.3%, whereas 47.6% of patients met the definition for treatment-resistance. Seropositive patients had twice the rate of treatment–resistance compared to seronegative patients (63.6% vs. 30.0%, P<0.0001). Moreover, in the seropositive group, the patients were older (47.6±12.2 vs. 39.81±12.01years, P<0.0001), had higher number of previous hospitalizations (13.9±11.7 vs. 9.6±8.5, P=0.0073), and increased Calgary depression scale for schizophrenia (CDSS) total score (7.8±4.5 vs. 6.3±3.8, P=0.012). There were no differences between the groups in the age of disease onset, smoking, positive and negative syndrome scale (PANSS) total, positive and negative scores, and the life-time history of suicide attempts.

Our results support the hypothesis that TG seropositivity might contribute to treatment-resistance in schizophrenia, at least in male patients.