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.

Beginning in August 2014, CDC received an increase in reports 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 reports of sporadic cases of AFM. From January 1 to August 31, 2016, a total of 50 people in 24 states across the country were confirmed to have AFM.

• From January 1 to August 31, 2016, 50 people were confirmed to have AFM. (Note: The cases occurred in 24 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 reported to and confirmed by CDC.
• There has been an increase in reports of confirmed AFM cases in 2016 compared with 2015 (21 cases in 16 states).

The graph shows reports of cases confirmed by CDC as of September 30, 2016.

It is currently difficult to interpret trends of the AFM data since reporting only started in 2014 and is voluntary in most states. Also, since AFM reporting 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 reporting is more awareness among and reporting by 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 information as they choose.

What we know about the AFM cases reported since August 2014:

• The patients’ symptoms have been most similar to those caused by certain viruses, including poliovirus, non-polio enteroviruses, adenoviruses, and West Nile virus. See a list of viruses associated with AFM(https://www.cdc.gov/acute-flaccid-myelitis/about-afm.html#germs).
  • 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 there were no cases of EV-D68 detected and so far in 2016, only limited sporadic cases of EV-D68(https://www.cdc.gov/non-polio-enterovirus/about/ev-d68.html) have been detected in the United States.

What We Don’t Know

What we don’t know about the AFM cases reported since August 2014:

• Despite extensive testing, CDC does not yet know the cause of the AFM cases.
• It is unclear what pathogen (germ) or immune response is causing the disruption of signals sent from the nervous system to the muscles causing weakness in the arms and legs.
• 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(https://www.cdc.gov/acute-flaccid-myelitis/about-afm.html#prevention) for information about how to protect your family from viral infections that may cause AFM

What CDC Is Doing

CDC is actively investigating the AFM cases and monitoring disease activity. We are working closely with healthcare providers and state and local health departments to increase awareness and reporting for AFM, and investigate the AFM cases, risk factors, and possible causes of this illness.

CDC activities include:

• encouraging healthcare providers to be vigilant for AFM among their patients, and to report suspected cases to their health departments
• verifying reports 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, respiratory 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 several medical institutions to review MRI scans of people from the past 10 years to determine how many AFM cases occurred before 2014.

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.