Currently, experts suspect an adenovirus is the culprit. So far, 77 per cent of cases in the UK tested positive for an active adenovirus infection, plus five of the nine cases in Alabama.
These infections are incredibly common – especially among children – but they usually cause cold symptoms, sometimes pneumonia. Only in rare cases in immunocompromised patients have they been known to cause hepatitis.
“That gives rise to the possibility that this might be an unusual or mutated adenovirus,” said Prof Kelly. “Although so far, it doesn’t look abnormal.”
Another, related theory is that the virus’s impact has been amplified by a lack of exposure to common adenoviruses during lockdowns.
But it’s not a slam dunk. In Denmark, where four cases have been confirmed, no children have tested positive, said Prof Anders Koch, infectious disease specialist at Denmark’s Statens Serum Institut.
“We haven’t seen the same signal with the adenovirus, but we have looked,” he told The Daily Telegraph. “So what you are seeing in England may be different from what you see in Denmark.”
According to the European Centre for Disease Prevention and Control (ECDC), only seven of the 30 cases detected on the continent have tested positive for an adenovirus, while three children had Covid. A few also tested positive for other viruses like rotavirus and influenza.
“The situation across the EU has unfolded since Easter,” said Erika Duffell, principal expert in hepatitis at the ECDC. “We’re updating our information on an hourly basis.” But experts warned we’re still in the “fog of war” – figures are murky as patients may not have all been tested for all viruses in the same way.
Some believe another, as-yet-unidentified infection may be to blame. “One possibility is there is a completely new infectious agent that we have not come across before,” said Prof Will Irving, a professor of virology at the University of Nottingham.
Or, suggested Prof Kelly, “we might find there is more than one virus behind it”.
“It’s hugely important to have an open mind that an adenovirus might not be the only factor here,” she said. “It may be too obvious – I hate to say that, but there may be more behind it.”
A side effect from coronavirus vaccines has also been ruled out, as none of the children affected in the UK have received a jab. While the case definition applies to children under 10, most in the UK are actually younger than five, so not yet eligible to receive a vaccine.
‘A myriad of symptoms’
In the meantime, paediatricians are focused on treating the children who end up on a hospital ward.
Doctors stress that most cases are relatively mild and self-resolve. They suspect that many cases have gone unnoticed, with children recovering without medical intervention. But, while no one has yet died, for some the prognosis is serious.
Dr Tassos Grammatikopoulos, a consultant in paediatric hepatology, works at King’s College Hospital in London – one of three specialist liver units in England, alongside Birmingham and Leeds. Since January, he’s treated a handful of the hepatitis patients.