The Centers for Disease Control and Prevention said on Friday that it is looking into the deaths of five children, linked to the growing number of mysterious pediatric hepatitis cases across the country.
The agency is investigating 109 cases in 24 states and Puerto Rico, Dr. Jay Butler, CDC’s deputy director for infectious diseases, said during a media briefing Friday. Cases date back to October, 2021.
The latest case count is a steep increase from two weeks ago, when just eleven such cases had been identified. Those cases prompted the CDC to issue a health alert for physicians nationwide to be on the lookout for unusual cases of hepatitis, or liver inflammation, in kids that didn’t have any obvious cause.
Butler said that of the 109 cases now under investigation, the vast majority have had to be hospitalized, and eight required a liver transplant. All were previously healthy, without underlying conditions.
In addition to the latest CDC report, at least 228 cases in 20 countries have been reported, according to the World Health Organization. No cause has been found that would link all of the cases.
“Investigators both here and across the globe are hard at work to determine the cause,” Butler said.
Adenovirus infections are not uncommon in kids, and typically cause a range of symptoms, from the sniffles to vomiting and diarrhea. But severe hepatitis linked to adenovirus is rare, and usually found only in chronically ill children.
The usual causes of hepatitis — hepatitis viruses A through E — have been ruled out. Children are not testing positive for COVID-19, and most are too young to have received the COVID vaccines.
Many of the new hepatitis cases have involved symptoms such as vomiting, dark urine and jaundice, or yellowing of the eyes and skin.
This story originally appeared on NBCNews.com.