There are no conclusive studies that identify the actual numbers of individuals specifically affected by AFM, but to date and since surveillance began in 2014, the Centers for Disease Control and Prevention (CDC) confirmed over 670 reports of those affected by AFM. Not all cases are reported to CDC nor confirmed by CDC, so this number is likely an underestimation. There have been reports of AFM in both children and adults, but AFM cases primarily affect children under the age of 18, with a median age of 6.3 years old. Less than 15% of all AFM cases occur in adults, although this may be an underestimate. Males may be more likely to be diagnosed with AFM. AFM confirmed cases and reports are regularly updated by CDC and can be viewed by state at https://www.cdc.gov/acute-flaccid-myelitis/cases-in-us.html.
Until the recent characterization of AFM in 2014, it is likely that many individuals with initial presentation of flaccid limb weakness and/or paralysis with predominantly grey matter lesions of the spinal cord were diagnosed with transverse myelitis or Guillain Barre Syndrome in previous years.