In 2014 in California, an outbreak of an illness that resembled polio was identified which retrospectively dated back to 2012. It is now called acute flaccid myelitis. All of the affected children (about 59 through July 2015) developed a rapid onset of paralysis in one or more limbs and MRI findings were consistent with injury to the central spinal cord. All of the children had been vaccinated against polio. Some of the children were positive for enterovirus -68, a virus known to be associated with limb paralysis and breathing difficulties. The CDC and researchers are currently trying to definitively determine the cause of this illness although they agree it is not polio.