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Acute flaccid myelitis (AFM) is a rare but serious condition. It affects the nervous system, specifically the area of the spinal cord called gray matter, which causes the muscles and reflexes in the body to become weak. This condition is not new. However, the large number of AFM cases reported since 2014, when we first started our surveillance for this condition, is new. The risk of getting AFM varies by age and year. We have seen increases in AFM cases every two years since 2014 and mostly in young children. Still, CDC estimates that less than one to two in a million children in the United States will get AFM every year. We think viruses likely play a role in AFM. Since 2014, most patients (more than 90%) had a mild respiratory illness or fever consistent with a viral infection before they developed AFM. All the stool specimens from AFM patients that we received tested negative for poliovirus. We are working closely with national experts to better understand the possible causes of AFM and update our information on treatment.

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CDC’s Investigation Updates

  • Most of the patients with AFM (more than 90%) had a mild respiratory illness or fever consistent with a viral infection before they developed AFM.
    • Viral infections such as from enteroviruses are common, especially in children, and most people recover. We don’t know why a small number of people develop AFM, while most others recover. We are continuing to investigate this.
  • These AFM cases are not caused by poliovirus; all the stool specimens from AFM patients that we received tested negative for poliovirus.
  • We detected coxsackievirus A16, EV-A71, and EV-D68 in the spinal fluid of four of 542 confirmed cases of AFM since 2014, which points to the cause of their AFM. For all other patients, no pathogen (germ) has been detected in their spinal fluid to confirm a cause.
  • Most patients had onset of AFM between August and October, with increases in AFM cases every two years since 2014. At this same time of year, many viruses commonly circulate, including enteroviruses, and will be temporally associated with AFM.
  • Most AFM cases are children (over 90%) and have occurred in 48 states and DC.
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