Clusters of Hepatitis of Unknown Origin and Etiology (Acute Non HepA–E Hepatitis) Among Children in 2021/2022: A Review of the Current Findings

Several clusters and individual cases of acute —often severe— hepatitis have been reported in Europe —mainly in the United Kingdom (U.K.)—, the United States (U.S.) and recently in Asia since October 2021. Laboratory investigation of the common viral hepatitis agents (HAV, HBV, HCV, HDV and HEV) yielded negative results prompting the use of the term “acute non hepA–E hepatitis” to describe this condition. The cases were characterized by the manifestations of acute hepatitis (abdominal pain, vomiting, diarrhea, jaundice and very high levels of liver enzymes) affecting children with a median age of 3–4 years. The exact underlying etiology has not been revealed yet; however, a leading hypothesis is that an infectious agent is the culprit underlying cause or at least a risk factor for acute non hepA–E hepatitis occurrence. So far, laboratory testing has shown the presence of adenovirus serotype 41 (Ad–41) which is classified in group F of adenoviruses in about three-fourths of the reported cases. However, the definitive link between adenoviruses and acute non hepA–E hepatitis has not been fully elucidated, which necessitates further investigation of this possible correlation. As of the end of April 2022, more than 200 cases were reported worldwide, the majority of which were in Europe: the U.K. (n=114), Italy (n=17), Spain (n=13), Israel (n=12), the U.S. (n=9), Denmark (n=6), Netherlands and Ireland (n=4), Japan (n=3), Austria, Belgium, France, and Norway (n=2), Germany, Poland, and Romania (n=1). Possible cases are being evaluated in Illinois, Minnesota, North Carolina, Wisconsin states of the U.S., Canada, Singapore and Slovenia. Vigilant surveillance and epidemiologic investigation to identify further cases are warranted at the global level to delineate the features of this emergent public health issue. The possible role of environmental and toxic agents including foodborne toxins should not be overlooked as well. Specific guidelines for identification of further cases is necessary particularly in low-income settings where testing for adenoviruses is not considered routinely. Genetic analysis of Ad–41 isolates is recommended to assess the potential changes in virus genome with subsequent possible altered virus behavior. Immunopathogenesis is another possibility that should be examined as well considering the absence of virus detection in liver biopsies of the affected children in the U.S.