AFM in the United States
At a Glance
- CDC is concerned about AFM, a serious illness that we do not know the cause of or how to prevent it.
- CDC is investigating the increase in AFM in 2016. As of December 2016, 138 people in 37 states were confirmed to have AFM.
- So far in 2017, CDC has received information for five confirmed cases of AFM.
- Even with an increase in cases in 2016, AFM remains a very rare disease (less than one in a million).
- CDC is concerned about the increase in cases in 2016.
- CDC is intensifying efforts to understand the cause and risk factors of AFM.
- It’s always important to practice general disease prevention steps, like washing your hands, staying up-to-date on vaccines, and protecting yourself from mosquito bites.
Acute flaccid myelitis (AFM) is a rare illness that anyone can get. It affects a person’s nervous system, specifically the spinal cord. AFM can result from a variety of causes, including viral infections.
Since August 2014, CDC has been made aware of an increased number of people across the United States with AFM for which no cause could be found. Since then, CDC has been actively investigating this illness. We continue to receive information about cases of AFM. From January 1 to December 31, 2016, a total of 138 people in 37 states across the country were confirmed to have AFM.
Updated April 21, 2017
^ Cases that CDC has been made aware of as of April 21, 2017 with onset of illness through December 31, 2016. The case counts are subject to change. CDC updates the case counts monthly with a one month lag to allow the time needed for case review.
* 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 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 on AFM case definitions, visit the Case Definitions page.
The graph shows the number of cases confirmed by CDC as of April 21, 2017 with onset of illness through December 31, 2016.
- From January 1 to December 31, 2016, 138 people were confirmed to have AFM. (Note: The cases occurred in 37 states across the U.S.)
- In 2015, 21 people were confirmed to have AFM. (Note: The cases occurred in 16 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 that have been sent to and confirmed by CDC.
- There has been an increase in reports of confirmed AFM cases in 2016 compared with 2015.
It is currently difficult to interpret trends of the AFM data since collection of information on cases only started in 2014 and is voluntary in most states. Also, since the collection of information on AFM cases is relatively new, there may initially be more variability in the data from year to year making it difficult to interpret or compare case counts between years. One possible reason for the differences in annual collection of information on cases is increased awareness of AFM among healthcare providers and health departments.
To protect patient confidentiality, CDC is not specifying the states with confirmed AFM cases. We defer to the states to release this information as they choose.
Number of confirmed AFM cases by year of illness onset, 2014-2016
|Year||Number confirmed cases||Number of states with confirmed cases|
*The case counts are subject to change.
What we know about the AFM cases for which CDC has received information:
- 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. See a list of viruses associated with AFM.
- Enteroviruses can cause neurologic illness, including meningitis. However, more severe disease, such as encephalitis and AFM, is not common. Rather, they most commonly cause mild illness.
- CDC has tested many different specimens from the patients for a wide range of pathogens (germs) that can cause AFM. To date, we have not consistently detected a pathogen (germ) in the patients’ spinal fluid; a pathogen detected in the spinal fluid would be good evidence to indicate the cause of AFM since this illness 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 with AFM, CDC did not consistently detect EV-D68 in the specimens collected from them. In 2015 no cases of EV-D68 were detected. CDC did not receive information about large outbreaks of illness associated with EV-D68 detections in the United States in 2016. But information about sporadic cases of EV-D68 infections were sent during that time. Learn more about EV-D68.
What we don’t know about the AFM cases for which CDC has received information:
- Despite extensive testing, CDC does not yet know the cause of these AFM cases.
- It is unclear what pathogen (germ) or immune response is causing the weakness and paralysis.
- CDC has not yet determined who is at higher risk for developing AFM, or the reasons why they may be at higher risk.
See Prevention for information about how to protect your family from viral infections 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 and encourage sending information about AFM cases to CDC. CDC actively investigates the AFM cases, risk factors, and possible causes of this illness.
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 using a case definition adopted by the Council of State and Territorial Epidemiologists (CSTE)
- testing specimens, including stool, blood and cerebrospinal fluid, from people confirmed to have AFM
- working with clinicians and state and local health departments to investigate and better understand the AFM cases, including potential causes and how often the illness occurs
- providing new and updated information to clinicians, health departments, policymakers, the public, and partners in various formats, such as the Morbidity and Mortality Weekly Report, the AFM website, and CDC social media
- pursuing an approach that uses 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, evaluating long-term outcomes of AFM cases, and updating treatment and management protocols.
For more information, see COCA Clinical Reminder (August 27, 2015) – Notice to Clinicians: Continued Vigilance Urged for Cases of Acute Flaccid Myelitis.
The 2014 investigation summary is available here: Acute Flaccid Myelitis in the United States—August – December 2014: Results of Nation-Wide Surveillance.
For more information on AFM surveillance, see the CSTE Standardized Case Definition for Acute Flaccid Myelitis.
- Page last reviewed: March 2, 2017
- Page last updated: April 20, 2017
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