According to the WHO, 169 unexplained cases of acute hepatitis, or liver inflammation, have been reported from across Europe and the Americas as of Friday. These include 114 incidences in the UK, 13 in Spain, 12 in Israel and 9 in the US. The WHO said: “It is not yet clear if there has been an increase in hepatitis cases, or an increase in awareness of hepatitis cases that occur at the expected rate but go undetected.”
All cases have been in children — with ages ranging from just one-month-old up to 16 years of age — and have exhibited markedly elevated liver enzymes.
Many of the patients reported experiencing initial gastrointestinal symptoms as abdominal pain, diarrhoea and vomiting.
Of these 169 cases, seventeen children — that is, around one-in-ten — have required a liver transplant and one death has been reported.
The common viruses that are known to cause acute hepatitis — hepatitis viruses A, B, C, D and E — were not detected in any of the cases, the WHO said.
However, doctors have detected adenovirus in 74 of the cases, and identified such as “F type 41” in 18 of these with information on molecular testing.
In addition, SARS-CoV-2 — the virus which causes COVID-19 — was identified in 20 of the cases, while 19 presented with a co-infection of adenovirus and SARS-CoV-2.
Adenoviruses are a broad family of some 50 viruses known to cause a wide variety of illnesses from the common cold, conjunctivitis, gastroenteritis, and bladder infection through to life-threatening multi-organ diseases in the clinically vulnerable.
The WHO said: “Common prevention measures for adenovirus and other common infections involve regular hand washing and respiratory hygiene.”
The implicated adenovirus type 41 typically manifests such symptoms as diarrhoea, fever, respiratory issues and vomiting — but has only ever previously been associated with hepatitis in immunocompromised children, not those that are otherwise healthy.
The WHO noted that the UK, the location of the majority of the outbreaks, and the Netherlands have both recently observed a significant increase in adenovirus infections.
Researchers have said that based on current information, it does not appear that the outbreaks are connected to international travel or links to other countries.
A WHO spokesperson said: “The UK first reported an unexpected significant increase in cases of severe acute hepatitis of unknown origin in young, generally previously healthy children.
“An unexpected increase of such cases has now been reported by several other countries — notably Ireland and the Netherlands.
“While adenovirus is currently one hypothesis as the underlying cause, it does not fully explain the severity of the clinical picture.
“Infection with adenovirus type 41, the implicated adenovirus type, has not previously been linked to such a clinical presentation.
“While adenovirus is a possible hypothesis, investigations are ongoing for the causative agent.”
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The WHO added: “Factors such as increased susceptibility amongst young children following a lower level of circulation of adenovirus during the COVID-19 pandemic, the potential emergence of a novel adenovirus, as well as SARS-CoV-2 co-infection, need to be further investigated.
“Hypotheses related to side effects from the COVID-19 vaccines are currently not supported as the vast majority of affected children did not receive COVID-19 vaccination.
“Other infectious and non-infectious explanations need to be excluded to fully assess and manage the risk.
“With continued new notifications of recent onset cases, at least in the UK, together with more extensive case searching, it is very likely that more cases will be detected before the cause can be confirmed and more specific control and prevention measures can be implemented.”
Going forward, the WHO and the European Centre for Disease Prevention and Control are supporting affected countries with investigations into the nature and origins of the disease.
Lines of inquiry include more detailed clinical and exposure histories, environmental and food toxicity testing, surveillance activities and further virological and microbiological tests.