Delirium – a state of acute confusion associated with a higher risk of serious illness and death – is a key symptom of Covid-19 in frail, older people, a new study indicates.

The findings highlight that doctors and carers should be aware of the condition as a possible early warning sign of Covid-19 in the elderly, even in the absence of more typical symptoms such as cough or fever, researchers say.

Led by clinical fellow and geriatrician Dr Rose Penfold at King’s College London, the researchers analysed data from two groups of older people aged 65 or over from March through to May.

The first group included 322 patients admitted to hospital with Covid-19 who had tested positive for the disease.

The second group was made up of 535 users of the Covid Symptom Study app who reported having had a positive test result.

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

Dr Penfold 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.

“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.”

Researchers found that older adults admitted to hospital who were classified as frail according to a standard scale were more likely to have had delirium as one of their symptoms than people of the same age not classed as frail.

According to the study, delirium, along with tiredness and breathlessness, was also more common in frailer users of the Covid Symptom Study app with Covid-19, compared with fitter people of the same age.

The study, published in the journal Age and Ageing, found a third of app users experiencing delirium did not report suffering the classic coronavirus symptoms of cough and fever.

However, delirium was the only symptom for around one in five (18.9%) of hospitalised patients.

Researchers suggest this is the first study showing delirium is a likely symptom of Covid-19 in frail, older adults.

But they add that the precise biological connection between the two conditions still needs to be understood.

The findings also highlight the need for systematic assessment of frailty for older people, along with awareness and screening for delirium for this vulnerable population in hospitals, care homes and the community.

Dr Claire Steves from King’s College London 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 (PPE) to protect this highly vulnerable group.”

Tim Spector, professor of genetic epidemiology at King’s College London and Covid Symptom Study lead, said: “In April we upgraded the Covid Symptom Study app to allow users to log health reports on behalf of friends and family who aren’t able to access the app.

“This significantly increased the number of older people in the study, providing vital insights.

“We’re hugely grateful to all our users and urge everyone to download the app and log their health and that of their loved ones on a daily basis as we move towards the winter months.”