The Determinants of Outcome of Severe Mental Disorders (DOSMeD) study, a global epidemiological study led by the World Health Organization, reported the annual incidence rate of schizophrenia from 1979 to 1980. In 2011, approximately 30 years later, we conducted a large-scale epidemiological study to investigate the incidence rate of first-episode schizophrenia in Nagasaki using the same method as the DOSMeD study. A telephone survey was conducted by researchers daily at 52 psychiatric hospitals, clinics, and institutes in Nagasaki. When a subject was confirmed, the researcher visited the medical facility in person to evaluate the patient’s symptoms. Of 441,706 people in Nagasaki City, 131 people were surveyed in the way, resulting in the diagnosis of psychosis in 25 patients, 20 of whom were determined to have schizophrenia. These data were used to calculate the incidence rates of psychosis (1.00 per 10,000 population; 95% confidence interval [CI], 0.54-1.46) and schizophrenia (0.80 per 10,000 population; 95% CI, 0.38-1.21). The 95% CI for the incidence rate of psychosis did not include the incidence rate for psychosis (broad definition) reported in the DOSMeD study (2.02). However, the 95% CI for the incidence rate of schizophrenia did include the incidence rate for schizophrenia (restrictive definition) reported in the DOSMeD study (1.01). Although the incidence rate of psychosis appeared to be decreasing, no significant change was found in the incidence rate of schizophrenia, comparing the present findings with those of the survey conducted 30 years ago. The incidence rate of schizophrenia is said to vary with changes in gender differences, racial differences, urbanization, and immigration; we therefore considered this possibility. In the future, it is necessary to carry out longer-term surveys covering multiple cities using the same methods
