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ObjectivesMajor depressive disorder (MDD) is often comorbid with other chronic and/or serious diseases. However, little is known about the prevalence of various diseases that are present before MDD onset. We examined the prevalence of all pre-existing diseases in the 12 months before an MDD diagnosis.DesignExploratory nested case–control study.SettingData, including diagnoses based on International Statistical Classification of Diseases and Related Health Problems, 10th revision codes, were from a Japanese health insurance database (JMDC).ParticipantsAdults newly diagnosed with MDD during 2015, 2016 or 2017 (but not the preceding year) (cases) were matched (exact) 1:10 to controls by age, sex, index date and working status.Primary and secondary outcome measuresThe primary outcome was the proportion of patients in each group with each pre-existing disease during the 12 months before the index date (ie, before MDD diagnosis in cases). Odds ratios (ORs) for onset of MDD were calculated for each pre-existing disease. A post hoc multivariate analysis examined interactions of metabolic risk factors (diabetes, hypertension, dyslipidaemia), psychiatric disorders (sleep disorders, psychiatric disorders other than depression) and MDD-related symptoms (headache, pain, autonomic nerve imbalance) on MDD diagnosis.ResultsThere were 13 420 cases and 134 200 controls (mean age 41.9 years; 66.5% male). The prevalence of almost all pre-existing diseases was higher in cases than in controls. The highest ORs (5.8–21.0) were for psychiatric diseases and sleep disorders. Insomnia (21.1% of patients; OR 8.7) and neurosis (9.7%; OR 10.6) were particularly prevalent in the case group. The odds of MDD increased in the presence of metabolic risk factors, psychiatric disorders and/or MDD-related symptoms.ConclusionsThere is a high prevalence of pre-existing diseases in Japanese patients who develop MDD compared with matched controls without MDD. These results suggest that patients with chronic and/or serious diseases should be actively monitored for depression.

Suicide is a major cause of death among inpatients with schizophrenia. However, there are only a limited number of surveys of suicide among such patients, especially in Asia. Therefore, we conducted a multi-institutional survey on suicide death among inpatients with schizophrenia in Japan. We investigated the characteristics of patients with schizophrenia who died by suicide during hospitalization in psychiatric wards, and simultaneously, those of patients with depression. Forty-five suicides of patients with schizophrenia occurred in 27 hospitals, and 46 suicides of patients with depression occurred in 33 hospitals. Hanging was the most common suicide method in both diagnostic groups. More than half of the patients with schizophrenia had histories of suicide attempts, although there was no significant difference in previous suicide attempts or self-harm between both diagnostic groups. Medical staff should confirm whether inpatients with schizophrenia have such histories. In this study, there was no significant difference in characteristics between inpatients with schizophrenia or depression. In order to prevent suicides of patients with schizophrenia during hospitalization, nonspecific suicide attempt prevention needs to be undertaken, such as ensuring comprehension of the general risk factors of suicide among medical staff.