The Centers for Disease Control and Prevention is investigating at least 109 cases of the disease in the United States. Similar diseases have been reported in at least two dozen countries, from Argentina to Denmark to Indonesia. There are approximately 450 reports worldwide, with the highest numbers in Britain and the United States.
Many cases are serious. Among the American children affected, more than 90 percent required hospitalization. Fifteen have required liver transplants. Five have died.
The disease appears to be concentrated in younger children. According to the CDC, most sufferers are under the age of 5, with the average age being just 2 years. Many are previously healthy children who have no known underlying medical conditions. Cases have been detected in 25 states and there is no clear geographical pattern.
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So far the cause is unknown. “Hepatitis” is a collective term for inflammation of the liver, for which there are many causes. The hepatitis A, B and C viruses (and more rarely the hepatitis D and E viruses) are known to cause liver inflammation. In adults, alcohol is another major cause of hepatitis. Certain drugs and toxins can also damage the liver and lead to severe inflammation. But none of the affected children tested positive for the hepatitis virus or had documented exposure to alcohol, drugs or toxins.
The only thing many have in common is a positive test for adenovirus, a common virus that causes the common cold, gastrointestinal upset, and other mild flu-like illnesses. The CDC said more than half of US cases tested positive for adenovirus, and the UK Health Security Agency reported that more than 70 percent of its cases did too. There is also a specific type of adenovirus, adenovirus 41, that has been found in many children in the United States, Britain and Europe.
The actual percentage of positive adenovirus cases could be even higher as cases may have been missed due to the way samples are collected. The CDC has issued a clinical alert to direct healthcare providers to be vigilant and use special methods for adenovirus testing.
Although adenovirus is a leading hypothesis, it may turn out to be merely an association, not a causation. Finally, adenoviruses typically do not cause liver inflammation in healthy people. They have also existed for years without any connection with acute hepatitis.
Still, there is precedent for an existing virus to induce a new syndrome. In 2012, a polio-like illness called acute flaccid myelitis suddenly emerged, causing weakness in the arms or legs in healthy children that often lasted for months or years. The frightening but extremely rare disease was eventually found to be linked to another common virus, a type of enterovirus. It remains unknown why most children who come into contact with the enterovirus experience runny noses and upset stomachs, while a very small minority have had serious consequences.
The adenovirus could behave similarly to an enterovirus, although given the timing of the coronavirus pandemic, there is active investigation into whether it is related to Covid-19. Some scientists have speculated that previous coronavirus infection could “trigger” an autoimmune response that could be exacerbated by subsequent adenovirus exposure. However, the coronavirus has only been identified in 18 per cent of reported cases in the UK. A CDC report on nine children hospitalized in Alabama found none of them had an acute Covid-19 infection or a documented history of previous infection.
Still others have questioned whether two years of masking and social distancing might have left children’s immune systems less able to fight off existing viruses. We do not know it. What we do know is that there is no link to the coronavirus vaccine as most children with this hepatitis are not old enough to be eligible for vaccination.
It will be some time before researchers find a cause. It is possible that one will never be found. The worrying thing for parents is that there is not much we can do to prevent this rare, alarming disease. If leading theories are correct, adenoviruses are exceptionally common, and the CDC estimates that 75 percent of children are already infected with the coronavirus.
However, parents can seek immediate medical attention for jaundice and encourage thorough hand washing to reduce the transmission of many diseases. And healthcare providers should be on high alert to conduct the necessary testing and notify state health officials accordingly.
As we have learned from the coronavirus pandemic, emerging diseases require surveillance, research and vigilance. Hepatitis is no different.