At a Glance
- CDC is concerned about AFM, a serious condition that causes weakness in the arms or legs.
- From August 2014 through January 2018, CDC has received information on a total of 320 cases of AFM across the US; most of the cases continue to occur in children.
- Even with an increase in cases since 2014, AFM remains a very rare condition. Less than one in a million people in the United States get AFM each year.
- It’s always important to practice disease prevention steps, such as staying up-to-date on vaccines, washing your hands, and protecting yourself from mosquito bites.
Acute flaccid myelitis (AFM) is a rare condition. It affects a person’s nervous system, specifically the spinal cord. AFM or neurologic conditions like it have a variety of causes such as viruses, environmental toxins, and genetic disorders.
Since August 2014, CDC has seen an increased number of people across the United States with AFM. We have not confirmed the cause for the majority of these cases. CDC has been actively investigating these AFM cases, and we continue to receive information about suspected AFM cases.
Updated April 30, 2018
^ Confirmed AFM cases that CDC has been made aware of as of March 31, 2018 with onset of the condition through January 31, 2018. The 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 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.
The graph shows the number of AFM cases confirmed by CDC as of March 31, 2018, with onset of the condition through January 31, 2018.
- So far in 2018, there is one confirmed case of AFM.
- In 2017, CDC received information for 28 confirmed cases of AFM. (Note: The cases occurred in 15 states across the U.S.)
- In 2016, 149 people were confirmed to have AFM. (Note: The cases occurred in 39 states across the U.S. and DC)
- In 2015, 22 people were confirmed to have AFM. (Note: The cases occurred in 17 states across the U.S.)
- From August to December 2014, 120 people were confirmed to have AFM. (Note: The cases occurred in 34 states across the U.S.)
- The case counts represent only those cases for which information has been sent to and confirmed by CDC.
It is currently difficult to interpret trends of the AFM data. Collecting information about suspected AFM cases is relatively new, and it is voluntary for most states to send this information to CDC. There may initially be more variability in the AFM data from year to year making it difficult to interpret or compare case counts between years.
We defer to the states to release additional information on cases as they choose.
Number of confirmed AFM cases by year of illness onset, 2014-2018*
|Year||Number confirmed cases||Number of states with confirmed cases|
|2016||149||39 (includes DC)|
*The case counts are subject to change.
Since 2014, CDC has learned the following about the AFM cases:
- Most patients are children.
- The patients’ symptoms have been most similar to complications of infection with certain viruses, including poliovirus, non-polio enteroviruses, adenoviruses, and West Nile virus.
- Enteroviruses most commonly cause mild illness. They can also cause neurologic illness, such as meningitis, encephalitis, and AFM, but these are rare.
- CDC has tested many different specimens from AFM patients for a wide range of pathogens (germs) that can cause AFM. To date, no pathogen (germ) has been consistently detected in the patients’ spinal fluid; a pathogen detected in the spinal fluid would be good evidence to indicate the cause of AFM since this condition affects the spinal cord.
- The increase in AFM cases in 2014 coincided with a national outbreak of severe respiratory illness among people caused by enterovirus D68 (EV-D68). Among the people confirmed with AFM, CDC did not consistently detect EV-D68 in every patient. During 2015, CDC did not receive information about large EV-D68 outbreaks in the United States, and laboratories reported only limited EV-D68 detections to CDC’s National Enterovirus Surveillance System (NESS). During 2016, CDC was informed of a few localized clusters in the United States. Learn more about EV-D68.
Among the people who were diagnosed with AFM since August 2014:
- The cause of most of the AFM cases remains unknown.
- We don’t know what caused the increase in AFM cases starting in 2014.
- We have not yet determined who is at higher risk for developing AFM, or the reasons why they may be at higher risk.
- We do not yet know the long-term effects of AFM. We know that some patients diagnosed with AFM have recovered quickly, and some continue to have paralysis and require ongoing care.
See prevention for information about how to protect your family from viruses that may cause AFM.
CDC is actively investigating AFM cases and monitoring disease activity. We are working closely with healthcare providers and state and local health departments to increase awareness for AFM. We are encouraging healthcare providers to recognize and report suspected cases of AFM to their health departments, and for health departments to send this information to CDC to help us understand the nationwide burden of AFM. CDC is also actively looking for risk factors and possible causes of this condition.
CDC activities include:
- urging healthcare providers to be vigilant for AFM among their patients, and to send information about suspected cases to their health departments
- verifying clinical information of suspected AFM cases submitted by health departments, and working with health departments and neurologists to classify cases using a case definition adopted by the Council of State and Territorial Epidemiologists (CSTE)
- testing specimens, including stool, blood, and cerebrospinal fluid, from suspected AFM cases
- working with healthcare providers, experts, and state and local health departments to investigate and better understand the AFM cases, including potential causes and how often the condition occurs
- providing new and updated information to healthcare providers, health departments, policymakers, the public, and partners in various formats, such as scientific journals and meetings, and CDC’s AFM website and social media
- using multiple research methods to further explore the potential association of AFM with possible causes as well as risk factors for AFM. This includes collaborating with experts to review MRI scans of people from the past 10 years to determine how many AFM cases occurred before 2014, updating treatment and management protocols, and engaging with several academic centers to conduct active surveillance simultaneously for both AFM and respiratory viruses.
For more information, see
- Page last reviewed: April 2, 2018
- Page last updated: April 19, 2018
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