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The Colorado Department of Public Health building is seen on Wednesday, August 11, 2021, in Glendale. (Olivia Sun, The Colorado Sun)

Colorado has reported its first cases of severe hepatitis of unknown cause in kids, adding to a growing number of cases nationally being investigated by the Centers for Disease Control and Prevention.

As of Friday, the Colorado Department of Public Health and Environment had reported five potential instances to the CDC. All met the CDC’s broad definition for cases — mainly that they occurred in kids ages 10 or younger and that doctors didn’t know what caused them. None of the five kids in Colorado died or required liver transplants as a result of their illnesses, though four were hospitalized. CDPHE says all five children either recovered or are in the process of recovering.

One case dates to December and was reported to the CDC last month. The other four cases were reported to the CDC over the past couple of weeks.

Several of the kids were treated at Children’s Hospital Colorado. Dr. Sam Dominguez, an infectious disease expert at the hospital, said not all of the kids have been severely ill but were instead sometimes admitted to keep their condition from worsening.

He said, despite the concern around the cases, they remain rare.

“I think there are lots of unanswered questions, and we’re still in the infancy of learning what’s going on here,” he said.

Only one of the children in Colorado tested positive for adenovirus, a common virus that is at the center of the leading hypothesis for what is causing the new cases of mystery hepatitis.

Beware of jaundice

Hepatitis is an inflammation of the liver, and it can have many causes. The best known causes are viral — Hepatitis A, B and C — but medications and other health conditions can also cause it.

The CDC said earlier this month that it had identified 109 potential cases across the country — the first ones having been seen in Alabama last fall. There have been five reported deaths nationwide, and 14 kids have required a liver transplant. Many of the stricken children require hospitalization and suffer from jaundice.

Dr. Sam Dominguez, an infectious disease specialist at Children’s Hospital Colorado, is seen in the hospital’s COVID-19 testing lab on April 22, 2020. (Provided by Children’s Hospital Colorado)

Dominguez said the kids in Colorado were usually brought in for jaundice — parents noticed their skin or eyes turning yellow. Some had previously had an illness with fever and diarrhea, but not all.

In a briefing with reporters, Dr. Jay Butler, the CDC’s deputy director for infectious diseases, said the number of cases identified so far is not above baseline levels, but disease investigators are watching closely because of how many of the cases have occurred in previously healthy children.

“Although rare, children can have serious hepatitis, and it’s not uncommon for the cause to be unknown,” Butler said.

Zooming in on adenovirus

A number of kids stricken with the mystery hepatitis, both in the United States and in the United Kingdom, have tested positive for a type of adenovirus known as adenovirus 41. Unlike most adenoviruses, which are respiratory bugs, adenovirus 41 attacks the digestive system. It has been known to cause hepatitis in kids who are immunocompromised, but it has not previously been known to cause hepatitis in kids with no known underlying health conditions, Butler said.

That’s just one of the mysteries surrounding the new cases. There’s no indication that adenovirus cases are surging, Butler said, though he acknowledged that the U.S. lacks the kind of robust case-tracking system that it has for COVID or even the flu.

Scientists are hoping to genetically sequence the adenovirus found in kids with hepatitis to see if it has picked up a significant mutation — but they’ve been having trouble doing so because the viral loads are so low when the kids are diagnosed. Butler said that may point to an immune response to the adenovirus infections as being the real cause.

COVID vaccines not to blame

Researchers are also trying to learn more about whether previous COVID-19 infections played a role, though, in a case study of nine kids from Alabama that the CDC released last week, none of the children had known prior COVID infections.

One thing Butler said is certain: COVID-19 vaccines almost certainly are not causing the cases. That’s because most of the children affected — “the vast majority,” Butler said — are too young to be vaccinated.

“COVID-19 vaccination is not the cause,” Butler said flatly.

So researchers continue to seek answers. Is there an environmental cause or maybe another, undiagnosed infection? Is it related to a medication? Is it something that happens every year but doctors — especially vigilant during a pandemic — are only just now picking up on?

“This is an evolving situation, and we’re casting a wide net to help broaden our understanding,” he said.

CDPHE, meanwhile, is also stepping up its tracking. Ordinarily, noninfectious cases of hepatitis are not things that doctors have to report to the state. But the agency last month sent out an alert to health care providers asking them to tell the state about any cases of pediatric hepatitis with an unknown cause.

Dominguez, the Children’s doctor, said parents will want to bring their kids in for medical help if they notice any yellowing of the skin or eyes or if their children have had an ongoing fever with diarrhea.

While worth being aware of, Dominguez said parents can take comfort in one thing.

“It’s still a relatively rare disease,” he said. “I think that’s the good news.”

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at...