Infections like bronchitis in children and adolescents have been linked with an increased risk of developing a mental illness later in life, a study has shown.

In the Jama Psychiarty study, researchers found being hospitalised for a serious infection increased the risk of hospital contact due to mental disorders by 84 per cent.

The risk of requiring psychotropic medication for all mental illnesses, excluding bipolar and depression, was also increased to 42 per cent after being hospitalised for an infection.

Infections treated with anti-infective agents, not requiring hospitalisation, were associated with increased risks of 40 per cent and 22 per cent, respectively.

More than one million people born in Denmark between 1995 and 2012 were analysed in the study, which also involved investigating the influence of genetics on risk.

The findings provided evidence for the involvement of infections in the immune system in causing a wide range of mental disorders in children and adolescents.

A detailed assessment showed the risks differed among specific mental disorders, being most elevated for OCD, mental retardation, and tic disorders.

These findings may be explained by consequences of infections on the developing brain and by other confounding factors, such as genetics or socioeconomic factors.

The increased risk for mental illness after infections was less severe when researchers analysed how genetics and home environment influenced patient conditions.

The authors also compared outcomes for over 800,000 siblings in this population — siblings who had infections with ones who did not — and found the increased risk for mental illness after hospitalization was just 21 per cent in the sibling that did not have an infection.

The risk of being prescribed a psychotropic medication after hospitalisation decreased from 22 percent to 17 percent.