Diarrhoea, vomiting and stomach pain should be considered as official symptoms of Covid-19 in children, scientists say.
The symptoms, which do not feature among the three listed by the NHS, have also been found to be relatively common in adults.
Officials have said, however, that they are too vague and that the system would be overwhelmed with worried people if everyone with a stomach ache thought they had Covid-19.
Scientists in Northern Ireland say the gut-related signs are so strongly linked to the illness in children that they should be considered.
But coughing – one of the top symptoms in adults who go on to become seriously ill – was not a reliable indicator of whether a child had coronavirus, they said.
Dr Tom Waterfield at Queen’s University Belfast told the BBC: ‘We are finding that diarrhoea and vomiting is a symptom reported by some children and I think adding it to the list of known symptoms is worth considering.’
Dr Waterfield and colleagues studied 992 children, of whom 68 had coronavirus. They had an average age of 10 years old.
Counting gastrointestinal symptoms – those affecting the stomach and bowels – would have significantly improved how many of the children could be diagnosed.
One of the key decisions health bosses have to make when deciding what is an official symptom is how many of the people with that symptom will actually have the disease, and how many will have something else.
They should also take into account whether the majority of people with the disease – in this case Covid-19 – could be found without including the symptom.
Only 34 of the children who had coronavirus in the Northern Irish researchers’ study had any symptoms.
By looking at children with fever, coughs and changes in smell or taste – the official Covid-19 symptoms – scientists correctly identified 76 per cent of children with the coronavirus.
When they added children who had stomach problems, however, this rose to 97 per cent – 33 out of the 34.
Because so many children didn’t get symptoms, and many of those who did did not have common ones, the experts said most of them wouldn’t ever be diagnosed.
Dr Waterfield and colleagues wrote: ‘This study demonstrates that approximately half of children are asymptomatic when infected with SARS-CoV-2 and that current UK testing strategies will fail to diagnose the majority of paediatric infections.’
The stomach and gut symptoms were reported in 13 out of the children, compared to 21 who were found to have a fever – fever was the most common sign.
By comparison, only six children lost their sense of smell or taste, which is listed as an official symptom by the NHS.
The health service in Britain has come under criticism for having too narrow a definition of the virus.
In America, the Centers for Disease Control and Prevention (CDC) lists 11 symptoms and someone with any of them can get tested.
Official policy in Britain is that, among members of the public, only those with one of the three main symptoms should get a test.
The Queen’s University team published their work on the pre-print website medRxiv without review from other scientists.