2.2. Study participants and sampling
In this case-control study, a total of 237 volunteers between 18 and 65
years old were enrolled in the schizophrenia or the healthy control
groups. One hundred seventeen patients with schizophrenia who applied to
the psychiatry department of Istanbul University-Cerrahpaşa, Cerrahpaşa
Medical Faculty in Istanbul were enrolled in the schizophrenia group of
the study. Schizophrenia is diagnosed clinically according to the
Diagnostic and Statistical Manual of Mental Disorders (DSM–5). Patients
diagnosing with schizoaffective or schizophreniform disorders were
excluded from this study. Also, possible suicide attempts of the
patients with schizophrenia were determined with the Suicide Behaviors
Questionnaire-Revised (SBQ-R) and clinical interviews. The healthy
control group was consisted of 120 participants without any psychiatric
disease or family history and having similar age and gender data with
the schizophrenia group. Two venous blood samples from each volunteer
were taken by venipuncture from a single cubital region and were
collected into plain and containing dipotassium
ethylenediaminetetraacetic acid (K2EDTA) vacuum tubes.
The tubes were filled and K2EDTA tubes were immediately
mixed with gentle 180° inversion. Serum samples were separated from
plain blood tubes by centrifugation at 2500 rpm and stored at -80°C
prior to T. gondii IgG analysis. Whole blood samples were also
stored at -80°C for the assessment of T. gondii DNA by molecular
methods.