The Centers for Disease Control and Prevention is investigating at least 109 cases of the condition in the United States. Similar illnesses have been reported in at least two dozen countries, from Argentina to Denmark to Indonesia. Worldwide, there are approximately 450 reports, with the highest numbers in Britain and the United States.
Many cases are severe. Among afflicted American children, 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 of those affected are under 5, with the median age being just 2 years old. 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.
Thus far, the cause is unknown. “Hepatitis” is a general term for inflammation of the liver for which there are many causes. The hepatitis A, B and C viruses (and, less commonly, the hepatitis D and E viruses) are known to induce liver inflammation. In adults, alcohol is another leading cause of hepatitis. Certain medications and toxins can also harm the liver and lead to severe inflammation. But none of the afflicted children tested positive for the hepatitis viruses or had any detected exposure to alcohol, medications or toxins.
The one thing many have in common is a positive test for adenovirus, which is a common virus that causes colds, gastrointestinal upsets and other mild flu-like illnesses. The CDC said that more than half of the U.S. cases tested positive for adenovirus, and the U.K. Health Security Agency reported that more than 70 percent of their cases have as well. There is also one specific type of adenovirus, adenovirus 41, that has been detected in many children across the United States, Britain and Europe.
The true percentage of positive adenovirus cases might be even higher, as cases could have been missed given the way the samples are collected. The CDC has issued a clinician alert to instruct health-care providers to be on the lookout and to use specialized methods for adenovirus testing.
While adenovirus is a leading hypothesis, it might turn out to be purely an association, not causation. After all, adenoviruses typically do not cause liver inflammation in healthy people. They have also existed for years without being linked to acute hepatitis.
Still, there is precedent for an existing virus to induce a new syndrome. In 2012, a polio-like condition called acute flaccid myelitis suddenly emerged, causing weakness in the arms or legs of healthy children that often persisted for months or years. The terrifying but exceedingly rare ailment was eventually found to be related to another common virus, a type of enterovirus. It remains unknown why most children who encounter enterovirus have runny noses and upset stomachs while a very small minority suffered severe outcomes.
Adenovirus could be acting similarly to an enterovirus, though given the timing of the coronavirus pandemic, there is active research into whether there is an association with covid-19. Some scientists have speculated that prior coronavirus infection could “prime” an autoimmune reaction that might be worsened by subsequent adenovirus exposure. But the coronavirus has been identified in only 18 percent of reported cases in Britain. A CDC report of nine children hospitalized in Alabama found that none of them had acute covid-19 infection or documented history of past infection.
Still others have questioned whether two years of masking and social distancing might have led to children’s immune systems being less capable of fighting off existing viruses. We don’t know. What we do know is that there is no association with the coronavirus vaccine, because most children with this hepatitis are not old enough to be eligible for vaccination.
It will take time for researchers to pin down a cause. It’s possible one might never be found. The disconcerting thing for parents is that there is not much we can do to prevent this rare, alarming ailment. If the leading theories are correct, adenoviruses are exceptionally common, and the CDC estimates that 75 percent of children have already contracted the coronavirus.
Parents can, however, seek immediate medical attention for jaundice and emphasize good hand-washing to reduce transmission of many diseases. And health-care providers should be on high alert to perform the necessary tests and notify state health officials accordingly.
As we learned from the coronavirus pandemic, emerging diseases require surveillance, research and vigilance. Hepatitis is no different.
