SCIENTISTS have warned a new symptom could be added to the official list of coronavirus symptoms.

They said suddenly feeling confused and delirious is a common symptom of Covid-19 among frail older people.

Officials in the UK don't recognise any symptoms other than coughing, fever and a lost sense of taste or smell, but there are many others that people suffer regularly.

Experts who run the Covid Symptom Tracker app, from King's College London, have now found that large proportions of elderly people get delirious when they're ill.

Delirium is a state that comes on suddenly in which people get confused, struggle to think clearly and may hallucinate, become agitated or have mood swings.

Echo: Suddenly feeling confused and delirious is a common symptom of Covid-19Suddenly feeling confused and delirious is a common symptom of Covid-19

Using self-reported symptoms from around 850 over-65s, the King's researchers found people official considered "frail" were three times as likely to become delirious.

And of over-65s who ended up in hospital because of Covid-19, one in five (18.9 per cent) said delirium was their only symptom.

The researchers said the coronavirus may be able to get into the brain and infect it, affecting someone's mental state.

Dr Rose Penfold, an epidemiologist at King's, said: "Older, frailer people are at greater risk from Covid-19 than those who are fitter, and our results show that delirium is a key symptom in this group.

SEE ALSO: What is coronavirus and what are the symptoms?

"Doctors and carers should watch out for any changes in mental state in elderly people, such as confusion or strange behaviour, and be alert to the fact that this could be an early sign of coronavirus infection."

The three main symptoms of a Covid infection are a new and continuous cough, a temperature above 37.8C and a change in smell or taste. About 85 per cent of people will have at least one of those symptoms.

However, research suggests certain age groups may also have other symptoms, such as diarrhoea and vomiting in children.

The team looked at data from 322 older people who were admitted to hospital with coronavirus between March and May, and also at 535 people who tested positive and used the Covid Symptom Tracker app during the same time period.

As well as considering the symptoms the over-65s reported - or had reported for them - the scientists looked at how frail they were.

Echo: Frail people with Covid-19 were more likely to have deliriumFrail people with Covid-19 were more likely to have delirium

This was done using a questionnaire for the app users or came from a standardised rating made by a doctor for patients who were in hospital.

People considered to be frail may be those who are physically weak, disabled, in poor health, or have brain damage such as that caused by dementia.

Most people living in care homes are considered frail, and they are also the group most at risk of dying if they catch coronavirus, which makes understanding the most common symptoms in that group important.

Frail people with Covid-19 were more likely to have delirium, tiredness and breathlessness than those who were the same age but stronger, the study found.

A third of people who reported having delirium on the app said they did not have the classic Covid-19 symptoms of coughing and fever.

Among the frail patients, 38 per cent had delirium, compared to just 12 per cent of the non-frail patients in the same age group, meaning it was three times more common.

The study found there were no significant differences in the rates of other common symptoms such as coughs or fevers between frail and non-frail groups.

Dr Claire Steves, a geriatrician in London and a lecturer at King’s College, said: "The past six months have shown us that Covid-19 can spread catastrophically through care homes.

"Knowing that delirium is a symptom in frail, elderly people will help families and carers spot the signs earlier of Covid-19 and act appropriately and put in place infection control measures such as isolation, increased hygiene and personal protective equipment to protect this highly vulnerable group."

The study, published in the journal Age and Ageing, adds to emerging evidence that the symptoms people experience when they catch coronavirus vary by age.

While middle-aged and older people - the group most likely to be admitted to hospital - often have the tell-tale cough or fever, others have them less often.

Young adults appear to often have no symptoms at all or to have just a mild flu-like illness.