In a health alert issued Wednesday, the Wisconsin Department of Health Services asked the state’s doctors to be on the lookout for these unusual cases and report them.
Wisconsin is the fourth state to announce that it is investigating cases of liver inflammation, or hepatitis, that doesn’t seem to be caused by any of the usual suspects like hepatitis A, B, C or D.
Alabama has reported nine cases in its cluster, including two children who needed liver transplants. Illinois has reported three cases, including one that required a liver transplant, and North Carolina says it has two cases that meet that definition.
The World Health Organization said Saturday that at least 169 cases of acute hepatitis in children have been identified in 11 countries, including 17 who needed liver transplants and one death.
The majority of the cases, 114, have been reported in the United Kingdom. There have been 13 cases in Spain, 12 in Israel, six in Denmark, fewer than five in Ireland, four in the Netherlands, four in Italy, two in Norway, two in France, one in Romania and one in Belgium, according to WHO.
The UK Health Security Agency says that roughly three-quarters of the 53 sick children who were tested for adenovirus there came back positive. The virus that causes Covid-19, on the other hand, was found in only a sixth of children who were tested — in line with the levels of community transmission in the UK.
Adenoviruses make up a large family of viruses that can spread from person to person, causing a range of illnesses including colds, pinkeye and gastroenteritis. They are only rarely reported as a cause of severe hepatitis in healthy people.
But these hepatitis cases come as the spread of adenovirus has escalated in recent months, along with other common viruses that have surged with the end of Covid-19 prevention measures and behaviors that kept most germs at bay.
After falling dramatically during the pandemic, documented adenovirus cases have roared back and are now at higher levels than the UK saw before Covid-19.
Although investigations are circling around adenovirus, how it might cause liver inflammation is still unclear. Experts say the virus may be just one factor that leads to these cases when it happens alongside something else.
CNN’s Michael Nedelman contributed to this report.