AFM Cases and Outbreaks

As of October 29, 2021, there have been 20 confirmed cases in 2021 out of 41 reports of patients under investigation (PUIs). In 2020, there were 32 confirmed cases out of 59 reports of PUIs.

There have been 670 confirmed cases since CDC began tracking AFM in August of 2014. CDC has been thoroughly investigating cases since that time. We have seen increases in AFM cases, mostly in young children, in 2014, 2016 and 2018.

Annual AFM Cases by State

Annual maps represent only cases for whom information was sent to and confirmed by CDC as of October 29, 2021. Patients under investigation are still being classified, and the case counts are subject to change. Cases of AFM have occurred in 50 states and the District of Columbia.

We defer to the states to release additional information on cases as they choose.

Cases by Month, 2014-2021

Most patients developed AFM between August and November, with increases in AFM cases in 2014, 2016, and 2018. Many viruses commonly circulate at this same time of year, including enteroviruses, which are likely responsible for the increase in cases in peak years.

Confirmed AFM cases by CDC

Confirmed AFM cases reported to CDC

^ Confirmed AFM cases by CDC from August 2014 through October 29, 2021. Case counts are subject to change.

* The data shown from August 2014 to July 2015 are based on the AFM investigation case definition: onset of acute limb weakness on or after August 1, 2014, and a magnetic resonance image (MRI) showing a spinal cord lesion largely restricted to gray matter in a patient age ≤21 years.

† The data shown from August 2015 to present are based on the AFM case definition adopted by the Council of State and Territorial Epidemiologists (CSTE): acute onset of focal or flaccid limb weakness and an MRI showing spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments, regardless of age.

For more information, visit the Case Definitions page.

Page last reviewed: November 1, 2021