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acute flaccid myelitis

Acute flaccid myelitis (AFM) is a rare but serious condition that affects the nervous system. It is characterized by a sudden weakness in one or more arms or legs, along with loss of muscle tone and reflexes.  Since 2012, there have been increases in AFM cases noted in the late summer and fall every two years.  Most cases occur in young children, and over 90% of the patients experience a mild respiratory illness and/or fever consistent with a viral infection prior to developing AFM. AFM has been linked to a variety of viruses including enteroviruses, such as enterovirus D68 and enterovirus A71. 

Even with an increase in cases since 2012, AFM remains a very rare condition. Less than one to two in a million people in the United States get AFM each year.


Most patients will have sudden onset of limb weakness and loss of muscle tone and reflexes. Some patients may also experience:

  • facial droop/weakness
  • difficulty moving the eyes
  • drooping eyelids, or
  • difficulty with swallowing or slurred speech.

If you or your child develops any of these symptoms, you should seek medical care right away.    


Although a viral etiology is suspected, it is still unknown why some people develop AFM while others experience only a mild respiratory illness. As such, there is no specific action to take to prevent AFM. However, it is always important to practice disease prevention steps, such as washing hands frequently, avoiding close contact with people who are sick, covering coughs and sneezes, and cleaning and disinfecting frequently touched surfaces.

To learn more about AFM, visit the CDC Acute Flaccid Myelitis website


Clinicians are encouraged to maintain vigilance for cases of AFM among all age groups. CDPH and the Centers for Disease Control and Prevention (CDC) conduct enhanced viral testing and surveillance for patients with AFM. If you are aware of a patient that meets the confirmed or probable case definitions below, please complete the following steps (detailed instructions are also provided in the CDPH AFM Quicksheet (PDF):

  1. Submit the AFM Patient Case Summary Form AND medical records listed on the form to the patient's local health jurisdiction (LHJ).
  2. Obtain approval from the local health jurisdiction (LHJ) for specimen testing.*
  3. After approval has been received, submit specimens with a completed General Purpose Specimen Submittal Form to the CDPH Viral and Rickettial Diseases Laboratory.  Local health jurisdictions will contact CDPH for the appropriate submittal form to submit specimens to CDC.

*Local health jurisdictions will contact CDPH for the AFM Patient Case Summary Form and to receive approval for testing.

Case Definitions


  1. Acute onset of focal limb weakness, AND:
  2. A magnetic resonance image (MRI) showing spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments**


  1. Acute onset of focal limb weakness, AND:
  2. Cerebrospinal fluid (CSF) with pleocytosis (white blood cell count >5 cells/mm3, may adjust for presence of red blood cells by subtracting 1 white blood cell for every 500 red blood cells present).
​​** A normal or negative MRI within the first 72 hours of onset of weakness does not exclude AFM as a diagnosis.
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