RESEARCH WEEKLY: Childhood Infections May Increase Risk of Developing Schizophrenia Spectrum Disorders

(December 11, 2018) Infections in childhood may increase the risk of developing schizophrenia spectrum disorders before adulthood, according to new research published this month.

The findings come at a time when research about the onset and progression of serious mental illness, including schizophrenia, is at a crossroads. Recent exploration of genetics as a once-promising contributor to disease development has proven limited and relatively unsuccessful, leaving researchers in search of the next avenue for investigation. And according to a growing group of studies, that avenue may be the immune system. Dr. E. Fuller Torrey, Treatment Advocacy Center founder and a pioneer in research on severe mental illness, first began writing about the implications of infections and mental illness more than 40 years ago.

In the newly published study, researchers in Denmark analyzed data from over one million Danish children and adolescents born between January 1995 and June 2012. They used national records to obtain information on the population's hospitalizations and prescriptions related to infection, as well as hospitalization for mental disorders and prescription of psychotropic medications. The study is the first of its kind to include even less severe infections-those treated on an outpatient basis with medication only-in its analysis and to consider the entire available medical history of study subjects.

child with mother and doctor The researchers found that individuals who had experienced an infection resulting in hospitalization were 84% more likely to be subsequently hospitalized for a mental disorder and 42% more likely to redeem a prescription for psychotropic medication. Even individuals who had never been hospitalized, but had been prescribed anti-infective medication such as an anti-biotic, saw an increased risk of psychiatric hospitalization (40%) and likelihood of treatment with psychotropic medication (22%).

Risk also increased as study subjects were treated with additional anti-infective prescriptions. Subjects who had been hospitalized and treated with 10 or more medications for infection were more than twice as likely to be hospitalized for a mental disorder and nearly twice as likely to be prescribed a psychotropic.

Mental disorders associated with the highest risk of onset following hospitalization for infection included personality and behavior disorders, such as paranoid personality disorder, and schizophrenia spectrum disorders.

The researchers suggest their results can be explained in a few different ways:

• Infections themselves may cause harm to the central nervous system, leading to increased risk of developing a mental disorder.

• Medications used to treat infections may negatively impact the gut microbiome, which ultimately negatively impacts the brain, leading to increased risk of mental disorder.

• Some individuals may just be genetically pre-disposed to both infections and mental disorders.

However, researchers also conducted additional analysis using only subjects for whom sibling data was available to control for genetic and socioeconomic factors. The risk of developing a mental disorder for this group after an infection-related hospitalization or use of anti-infective medication was lower, but still significant. According to the researchers, genetics may be relevant in interpreting results, but variation in risk is more likely due to the effects of infection or anti-infection medications on the brain.

While this research does not mean a child with a nasty habit of catching strep throat is going to be diagnosed with schizophrenia, it does suggest that further research into the body's immune response could be beneficial in understanding the onset and development of mental illness.