ONE in three Covid survivors was diagnosed with a neurological or psychiatric disorder within six months of their infection, according to the largest study to date on the effects of the disease on the brain.

Patients admitted to hospital, particularly those who required intensive care, were more likely to go on to suffer a stroke or develop dementia.

However, three in every 1000 Covid patients who had never been hospitalised were found to have suffered a brain haemorrhage and nearly one in 100 developed a psychotic illness.

The study, published today in the journal Lancet Psychiatry, analysed more than 236,000 health records in the US of patients aged older than 10 years old who had a confirmed Covid infection between January 20 and December 13 2020 and were still alive six months later.

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Previous coronavirus pandemics have been associated with an increased incidence of psychiatric and neurological problems, but the picture for Covid has been unclear.

Overall, the researchers from Oxford University estimated 34% of people were diagnosed with a neurological or mental health disorder following Covid.

One in 10 of these individuals had no medical history of these conditions.

Anxiety, mood and substance misuse disorders were the most common diagnoses, followed by insomnia.

Brain haemorrhages occurred in 0.6% of patients overall, with strokes and dementia in 2.1% and 0.7% of patients respectively.

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The risk was higher in hospitalised and intensive care patients, and particularly acute among those who developed delirium as a result of encephalopathy - swelling on the brain - during Covid.

For example, 7% of Covid patients who suffered encephalopathy went on to develop a psychotic disorder, such as schizophrenia or bipolar disorder, compared to 0.9% of those who were never hospitalised.

HeraldScotland: Patients admitted to intensive care, especially those who developed delirium, were at highest risk of subsequent psychiatric and neurological illnessesPatients admitted to intensive care, especially those who developed delirium, were at highest risk of subsequent psychiatric and neurological illnesses

Four in every 1000 Covid patients diagnosed with a psychosis had no prior medical history of hallucinations and delusions.

In relation to dementia, the incidence was 4.7% compared to 0.4% without hospitalisation.

Professor Paul Harrison, lead author of the study, said: “Although the individual risks for most disorders are small, the effect across the whole population may be substantial for health and social care systems due to the scale of the pandemic and that many of these conditions are chronic."

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Comparisons with a control group of influenza and respiratory tract patients found that those with Covid compared to flu were 44% more at risk of neurological and mental health diagnoses, and a 16% more at risk than those with respiratory tract infections.

Dr Max Taquet, a co-author of the study, said: “Our results indicate that brain diseases and psychiatric disorders are more common after Covid-19 than after flu or other respiratory infections, even when patients are matched for other risk factors. We now need to see what happens beyond six months.”