herring because the viruses are so common among children it is difficult to determine whether they are the cause of these hepatitis cases or whether many of the children have been infected incidentally for proof of causality you really need a lot of data which we just dont have dr malley saidhow are officials respondingthe cdc is pursuing multiple lines of investigation dr butler said first the agency is trying to determine whether these cases truly represent a new spike in unexplained hepatitis in children or are part of an existing phenomenon that is now being recognized in the light of increased awarenessa preliminary analysis suggests that in the united states 1500 children to 2000 children under age 10 are admitted to hospitals annually for hepatitis cases that are not linked to a known viral cause dr umesh parashar chief of the cdcs viral gastroenteritis branch said at the briefing on friday so far the agency has not documented an overall increase in cases though a small increase might be difficult to detect he notedthe agency is also working with doctors across the country to gather more data this effort includes reviewing the medical records of children who have had hepatitis previously and searching for any exposures or patterns that might tie the new cases together this is the type of shoeleather epidemiology that our disease detectives are trained to do dr butler saidthe cdc is also investigating whether adenovirus infections are more common among children with liver disease than in children without liver disease and conducting laboratory studies of adenovirus samples from affected children early evidence suggests that multiple versions of adenovirus 41 may be involved dr butler saidis this connected to covid19its not clear of the 169 cases in the who report 20 tested positive for the coronavirus and there was evidence of coronavirus infection in fewer than 20 percent of the us cases dr butler said these figures are not surprising given how widely the virus has been spreading in recent months scientists saidthere is no evidence that hepatitis is linked to the covid19 vaccines the vast majority of these children are unvaccinated and most are too young to have received a vaccine anyway dr butler saidstill a coronavirus connection cannot be entirely ruled out experts cautioned it is possible that a prior coronavirus infection could be a contributing factor and the hepatitis cases may be linked to the pandemic in less direct ways for example the public health measures implemented over the past two years may have left fewer children exposed to common adenoviruses that in turn might have made them more susceptible now according to one of the uk health security agencys working hypothesesbut that too is speculativeat this point dr shiau said we still dont know whats going on