The agency said it has not identified a confirmed cause for AFM. It said more than 90 percent of patients with AFM had a mild fever or respiratory illness consistent with a viral infection, such as enteroviruses, before they developed the condition.
The CDC is continuing to investigate why a small number of people develop AFM and most others recover.
Despite the illness being compared to polio, the CDC said it is not caused by poliovirus.
More information is at CDC.gov.