Heart disease is the leading cause of death in Denmark, where it accounted for at least 31% of all deaths from 1970 to 2002.¹ During the 1990s and 2000s, the mortality from heart disease in Denmark and the United States declined owing mainly to improved treatment, such as the use of new pharmacological treatment of myocardial infarction, and to a lesser degree because of improvement in primary prevention.^2-5

Suicide and death by accidents in persons with schizophrenia and bipolar disorder are common, but excess mortality from natural death accounts for even more years of life lost. The impact of somatic comorbidity, however, often is not duly considered in analyses and explanations of excess mortality in patients with psychotic disorders. This study investigates and evaluates the impact of 19 severe chronic diseases on excess mortality due to diseases and medical conditions (natural death) in individuals with psychotic disorders compared with the general population using a population-based cohort study in Denmark. Incidence/mortality rate ratios of admission/mortality were calculated using survival analysis. Cohort members with psychotic disorders had higher incidence rates of hospital contacts for almost all of the 19 disorders than the general population. The mortality rate ratio (MRR) of natural death was 7.10 (95% CI 6.45, 7.81) for schizophrenic men, decreasing to 4.64 (95% CI 4.21, 5.10) after adjustment for the somatic disorders. The same pattern existed in women and in both genders with bipolar disorder. Highest MRRs were observed for psychotic patients without hospital admissions with the investigated somatic disorders. Chronic somatic diseases accounted for half of the excess mortality in patients with schizophrenia or bipolar disorder. Chronic disorders investigated in this paper seem to be under-treated or under-detected among such patients.

Previous studies^1-3 of adults have indicated that severe infections are associated with an increased risk of mental disorders. Potential mechanisms include direct influences of infections in the central nervous system, immune activation, and inflammatory mediators,^4,5 as well as alterations in the microbiome.⁶ A possible role for infection and inflammation in the pathogenesis of severe mental disorders is also supported by genetic studies^7-9 documenting an increased risk associated with immune-regulatory genes.

Identification of patients at high risk of treatment-resistant schizophrenia at the time of schizophrenia diagnosis would be of great clinical benefit in minimising the delay to clozapine treatment in patients unlikely to respond to non-clozapine antipsychotics. However, little is known about predictors of treatment resistance in this patient population. We used a treatment-based proxy for treatment-resistant schizophrenia to identify candidate predictors of treatment resistance at first hospital contact with a schizophrenia diagnosis. In this population-based cohort study, we obtained Danish national registry data for all adult patients (≥18 years) with incident schizophrenia diagnosed between Jan 1, 1996, and Dec 31, 2006, and followed up until Dec 31, 2010. Our main proxy definition of treatment-resistant schizophrenia was the earliest instance of either clozapine initiation or hospital admission for schizophrenia after having had two periods of different antipsychotic monotherapy. We did multivariable Cox proportional hazards regression analysis to estimate the association between baseline candidate predictors and treatment resistance. 8624 patients fulfilled the criteria for inclusion. In multivariable complete-case analyses, 1703 (21%) of 8044 patients fulfilled the main proxy definition of treatment-resistant schizophrenia during a median follow-up of 9·1 years (IQR 6·3-11·9). Younger age (hazard ratio 0·96 [95% CI 0·95-0·97]), living in a less urban area (provincial 1·38 [1·23-1·56], rural 1·44 [1·25-1·65]), primary education level (0·88 [0·79-0·98]), more than 30 bed-days in psychiatric hospital in the year before first schizophrenia diagnosis (1·54 [1·35-1·75]), inpatient at first schizophrenia diagnosis (2·07 [1·87-2·29]), paranoid subtype (1·24 [1·13-1·37]), comorbid personality disorder (1·24 [1·11-1·39]), psychotropic drug use (antipsychotics 1·51 [1·35-1·69], antidepressants 1·15 [1·03-1·29], and benzodiazepines 1·22 [1·10-1·37]), and previous suicide attempt (1·21 [1·07-1·39]) were all significantly associated with treatment-resistant schizophrenia. Our study identifies several candidate predictors that could potentially be included in future prediction models for treatment-resistant schizophrenia. Notably, established risk factors for schizophrenia did not predict treatment resistance, suggesting that treatment-resistant disease might be a distinct subtype of schizophrenia and not merely a more severe form. European Community's Seventh Framework Programme.