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People admitted to hospital with an infection face a higher risk of being diagnosed with a range of brain and mental health conditions over the following two years, according to a new study led by researchers at the University of Oxford.
Published in the journal JAMA Psychiatry and supported by the National Institute for Health and Care Research (NIHR) Biomedical Research Centre: Oxford Health, the study analysed electronic health records from 62 healthcare organisations in the United States, including more than 1 million matched pairs of patients. Researchers compared people hospitalised with infections affecting different parts of the body, such as the lungs, urinary tract, skin, liver, heart, gastrointestinal system, and brain, with similar people hospitalised for non-infectious reasons.
The team found that hospitalised infections were followed by higher risks of most of the 14 psychiatric and neurological outcomes studied. These included anxiety, mood and psychotic disorders, insomnia, cognitive problems, dementia, seizures, stroke, brain haemorrhage, and nerve or muscle disorders.
The strongest relative increase was seen for encephalitis, an inflammation of the brain. People hospitalised with an infection were five times more likely to develop encephalitis than those hospitalised for another reason. However, the largest absolute increase was seen for cognitive problems, meaning that memory and thinking difficulties accounted for the greatest additional burden after infection.
Risks were seen across age groups, including in children, but they were smaller in children than in adults. Older adults were particularly affected.
The study also compared different types of infection with each other. Infections directly affecting the brain, such as infectious encephalitis, were among the strongest risk factors for most later disorders.
The findings suggest that infections may affect brain health through multiple mechanisms. These could include direct injury to the brain, inflammation, blood–brain barrier disruption, vascular injury, immune activation, or indirect effects of severe illness and hospitalisation. The study does not prove that infections directly cause these later conditions, but it provides a broad map of where risks are greatest and where mechanistic research should focus.
The results also have implications for pandemic preparedness. When a new infectious disease emerges, health systems often have little guidance on which longer-term brain and mental health problems to anticipate. This study suggests that the body system affected by an infection could help provide an early warning map of possible post-infectious complications.
Lead author Maxime Taquet, Associate Professor in the Department of Psychiatry at Oxford and NIHR Academic Clinical Lecturer says:
These findings provide the first map linking infections of different parts of the body with neurological and psychiatric consequences. This map will help prepare for future pandemics and outbreaks, and provides key information for studies aiming to understand the mechanisms by which an infection might have consequences in the brain.”
Senior author Professor Paul Harrison, Professor of Psychiatry at the University of Oxford, said: “Our findings highlight the need to understand how and why many infections seem to increase the risk of many psychiatric disorders. In this way potential new treatments may be identified. “
The study used routinely collected electronic health records, which can miss or misclassify diagnoses. It also focused on infections severe enough to require hospitalisation, so the findings may not apply to milder infections managed in the community. Although the analyses adjusted for many differences between patients, residual confounding cannot be ruled out, and the study cannot prove causation.