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Mystery hepatitis outbreak in kids: Which states are investigating cases?

Minnesota, Wisconsin, South Dakota, North Dakota and Illinois are among the states that are investigating cases.

A pediatric hepatitis outbreak with mysterious origins is continuing to grow, as more U.S. states investigate cases of kids developing the liver illness without a known cause.

In a statement Wednesday, the Centers for Disease Control and Prevention said the agency is investigating 180 cases in 35 U.S. states and Puerto Rico. The cases have all occurred since October 1.

At the CDC's last count on May 5, 109 cases were being investigated, but the agency stressed that the increase doesn't mean more cases are appearing; many of the new cases under investigation are not recent and may not end up being linked to the outbreak.

The CDC is also investigating five deaths linked to the outbreak, which all occurred before February. As of May 5, only 9% of children have needed liver transplants, down from 15%.

Worldwide, at least 450 such cases have been reported in 27 countries, according to the European Centre for Disease Prevention and Control, a European Union agency.

Hepatitis refers to an inflammation of the liver, which is usually caused by one of the hepatitis viruses — hepatitis A, B, C, D and E —but in these recent cases, these viruses were ruled out as the cause.

The first reported cases in the U.S. were in Alabama in October. The CDC issued an alert and a report on the cluster of nine cases. All of the children, between 1 and 6 in age, tested positive for adenovirus, which the CDC and WHO are investigating as a possible cause of the global outbreak.

In its Wednesday statement, the CDC said adenovirus has been identified in nearly half the 180 children and "continues to be a strong lead."

Adenoviruses are common, usually causing cold-like and gastrointestinal symptoms. Prior to these cases, adenoviruses were not known to cause hepatitis in otherwise healthy children, per the CDC. In all of the U.S. cases under investigation, the children were previously healthy with no underlying conditions.

“There’s no link to one geographic area, common exposure to particular foods or animals, travel or to toxins,” Dr. Philippa Easterbrook, an infectious disease physician with the World Health Organization, said during a media briefing on May 4.

Most of the children are too young to have received the COVID-19 vaccine, so there is no evidence it has played a role in the illnesses. But the CDC said it is investigating whether a prior COVID-19 infection may be involved, as a recent paper in The Lancet suggests.

The following states are investigating cases of pediatric hepatitis with an unknown cause:


The first report the CDC issued on the mysterious hepatitis focused on a cluster of nine cases spread across different parts of Alabama.


The Minnesota Department of Health is investigating "several cases" of hepatitis in kids with an unknown cause, local NBC affiliate KARE 11 reported in late April.


As of late April, the Wisconsin Department of Health is investigating at least four cases of unusual hepatitis in children, including one death and one liver transplant.

South Dakota

The South Dakota Department of Health is investigating a case in a child under 10 years old in Brown County, it announced Wednesday.

North Dakota

A child in Grand Forks County is recovering at home after being hospitalized with hepatitis with an unknown cause, the North Dakota Health Department announced Thursday.


The Illinois Department of Health announced in late April that it is investigating "three suspected cases of severe hepatitis in children under ten years of age, potentially linked to a strain of adenovirus. Two of the cases are in suburban Chicago and one is in Western Illinois."


Doctors at Cincinnati Children’s Hospital in Ohio told NBC News that they had treated at least six cases in kids between 18 months and 10 years old, all of whom were from Ohio. One child needed a liver transplant.


One case is being investigated in Delaware, NBC News reported in late April.


The health department in Georgia said it was also investigating a "handful" of cases as of late April, according to NBC News.


In late April, NBC News reported one case was being investigated in Louisiana.

New York

New York health officials are investigating a "handful" of cases of hepatitis in kids with an unknown origin, NBC News reported in late April.

North Carolina

Two cases of the rare liver inflammation were reported in school-age children in North Carolina, local NBC affiliate WCNC reported in late April.


The Tennessee Department of Health has reported six cases as of late April, according to NBC News.


The California Department of Public Health told TODAY in a statement on May 5 that it has "received reports of seven young children in California with severe hepatitis since October 2021. We do not know yet if adenovirus played a role in these rare illnesses or if these cases are connected."


The Idaho Department of Health is currently investigating two cases pediatric acute hepatitis of unknown origin, it told TODAY in a statement.


University of Texas Health San Antonio has "seen cases of a mysterious and serious liver disease in otherwise healthy children" in South Texas, according to a statement.

The Texas Department of State Health Services told TODAY in a May 6 statement that the state has no confirmed cases of pediatric hepatitis associated with adenovirus 41. "We are aware that some local health departments are investigating cases of pediatric hepatitis to determine if they are associated with adenovirus type 41," it said, adding that the investigations are ongoing.


In a May 6 statement, the Colorado Department of Health told TODAY that it has reported four cases of hepatitis in kids 10 and younger with an unknown cause to the CDC.

In the first case, which dates back to December, the patient tested negative for adenovirus and has since recovered. In two out of the three new cases, the patients were hospitalized, and one tested positive for adenovirus. None required liver transplants, and all are recovered or improving. The cases were all in different parts of the state, according to the statement.


A spokesperson for the Missouri Department of Health told TODAY via email that the state is investigating cases, but none are confirmed at this time.


"We continue to investigate reports from Maryland providers but have not yet reported any confirmed cases," a spokesperson for the Maryland Department of Health told TODAY in a May 6 statement.


"Indiana currently has four pediatric patients with non-viral hepatitis under investigation. Please note that this is an ongoing investigation, so these are not confirmed cases at this time," an Indiana health official told TODAY in a May 6 statement.

Washington state

A spokesperson for the Washington State Department of Health told TODAY in a statement, "We are aware of the situation and are currently investigating."


The Pennsylvania health department is investigating "multiple cases for a possible connection" to the ongoing pediatric hepatitis outbreak of unknown origin but has not confirmed any, according to a statement to TODAY.


Arkansas Department of health is "investigating one potential case, but more investigation is necessary," a statement to TODAY read.


Two patients in Michigan meet the CDC's criteria for being investigated as possibly part of the outbreak, a spokesperson for the Michigan Department of Health and Human Services told TODAY.


Arizona is investigating one patient as part of the CDC's inquiry into cases of pediatric hepatitis with an unknown cause, a health official told TODAY.


The Hawaii Department of health is investigating one report of "acute pediatric hepatitis of unknown origin in a Maui resident under 10 years of age," a spokesperson told TODAY in a May 7 statement. The child was hospitalized for several days at the end of April with fever and abdominal pain, and the case was reported to the state's health department last week. A number of lab test results are outstanding, and no cause has been determined. Hawaii's health department is working with the CDC to identify the cause.


Florida is one of the 24 states where the CDC is investigating cases, the agency said, but as of May 6, there are no confirmed cases in the state, according to a statement from the Florida Department of Health to TODAY.


The CDC said Nebraska is one of the 35 states where it is investigating cases.


Two cases of pediatric hepatitis are being investigated by the Massachusetts Department of Public Health, NBC Boston reported. Both children tested negative for adenovirus.


In a May 17 statement, the Virginia Department of Health told TODAY that it has two patients under investigation for acute hepatitis with an unknown cause. The illnesses occurred between January and March. They were from the Eastern region of the state and were hospitalized but have since recovered.


Kentucky is one of the 35 states with cases under investigation by the CDC.


Nevada is one of the 35 states with cases under investigation by the CDC.

New Jersey

New Jersey is one of the 35 states with cases under investigation by the CDC.


Oklahoma is one of the 35 states with cases under investigation by the CDC.

Rhode Island

Rhode Island is one of the 35 states with cases under investigation by the CDC.

Which states have not reported cases?

The following states do not have any cases under investigation by the CDC:

  • Mississippi
  • Maine
  • Vermont
  • Wyoming
  • South Carolina
  • Montana
  • New Mexico
  • Utah
  • Oregon
  • Alaska
  • Connecticut
  • Iowa
  • Kansas
  • New Hampshire
  • West Virginia

What symptoms should parents look for?

Adenoviruses and hepatitis can both cause nausea and diarrhea, but adenoviruses "typically run their course without needing medical intervention,” Dr. David Hill, a Wayne County, North Carolina-based pediatrician and the official spokesperson of the American Academy of Pediatrics, previously told TODAY.

In children experiencing these symptoms, keep an eye out for severe abdominal pain, fever, dark-colored urine or light-colored stool, and the most telling symptom: yellowing coloring in the skin or whites of the eyes, also known as jaundice.