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. CDC has been thoroughly investigating the AFM cases that have occurred since 2014, when we first noted a large number of cases being reported.
What CDC has learned since 2014
- 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 484 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 46 states and DC.
We work closely with national experts, healthcare providers, and state and local health departments to thoroughly investigate AFM by looking for possible risk factors and causes, figuring out why some people develop this condition, monitoring AFM activity nationwide, and updating possible treatment options. Specific activities include:
Obtaining National Data and Monitoring AFM Activity
- Encouraging healthcare providers to recognize and report to their health departments all patients who they suspect may have AFM, then for health departments to send this information to CDC to help us understand AFM activity nationwide
- Conducting enhanced surveillance for AFM by initiating a study at seven pediatric hospitals across a geographically diverse area of the United States. These hospitals are also conducting surveillance for acute respiratory and gastrointestinal illness and collecting samples for viral testing. Enhancing AFM surveillance at these hospitals will allow a comparison of AFM case counts with current circulating respiratory and gastrointestinal viruses in these locations
- Supporting states that want to confirm their own cases, by providing standard operating procedures, a medical chart abstraction tool, and training on how to interpret the information. We also created a secure database to collect medical information including symptoms, findings from their clinical exam, treatment, and laboratory test results
- Collaborating with experts to review MRI scans of people from the past 10 years to estimate how many AFM cases occurred before 2014
Confirming Cases of AFM
- Verifying clinical information of patients under investigation (PUIs) for AFM submitted by health departments, and working with health departments and neurologists to classify cases using a standard case definition adopted by the Council of State and Territorial Epidemiologists (CSTE)
Exploring Treatment Options
- Providing “Interim Considerations for Clinical Management of Patients with AFM”, in consultation with national experts in infectious diseases, neurology, pediatrics, critical care medicine, public health epidemiology, and virology. We initially developed this document in November 2014, when we first noted a large number of cases being reported. After four years of best practices in patient care and treatment experience, we updated the document and released it in November 2018.
Laboratory Testing of Specimens from PUIs for AFM
- Testing specimens, including stool, blood, and spinal fluid, from PUIs for enteroviruses and other viruses
- Collecting data from laboratories outside of CDC about their testing results to complete records of laboratory test results for all PUIs
- Using metagenomic sequencing approaches to identify known and unknown pathogens (germs) not currently considered in the EV-D68 specifically targeted approaches
- Developing assays to look for biomarkers associated with AFM for earlier identification of children at risk of becoming paralyzed
- Investigating how damage to the spinal cord in AFM patients could occur days or weeks after an infection to understand how viruses may be causing this disease
Consulting with experts to better understand AFM
- Establishing an AFM task force to foster collaborations between CDC and the scientific community to better understand what’s causing AFM, how to prevent it, and how to treat it (see press release)
- Hosted a one-day technical consultation in September 2017 with 12 nationally-recognized experts in AFM and 20 CDC medical officers, epidemiologists, and laboratory scientists to discuss how viruses could cause AFM and what viruses were most likely responsible
Educating healthcare providers and the public
- Working with health departments to educate healthcare providers in every state so they are aware of the symptoms of AFM, how to report PUIs, what specimens to collect, and the clinical management considerations for patients with AFM. Some educational activities and materials include health alerts, job aids, toolkits, webinars, and scientific publications and presentations.
- Updating our AFM website regularly with new information about AFM, and current counts of confirmed AFM cases. This website has information about AFM and CDC’s investigation, and a section for healthcare providers with information about the AFM case definitions, data collection and reporting of PUIs, specimen collection and shipping, and clinical management of patients
- Publishing data and findings of our AFM investigation in scientific journals, and presenting at scientific conferences
AFM is a complex condition, and it is difficult to determine why only some people go from having a mild respiratory illness or fever to developing AFM.
- Since AFM affects the spinal cord, finding a pathogen (germ) in the fluid that surrounds the spinal cord would be good evidence for a cause. CDC has tested many different specimens from AFM patients for a wide range of pathogens that can cause AFM. We detected coxsackievirus A16, EV-A71, and EV-D68 in the spinal fluid of four AFM cases out of 484 confirmed cases since 2014, which points to the cause of their AFM. For all other patients, no pathogen (germ) has been detected in their spinal fluid. The absence of a pathogen in most AFM cases means we haven’t found the definitive cause yet. There could also be something else triggering the patient’s AFM, such as their immune response to an infection or a genetic factor that may make them more susceptible.
- Respiratory illnesses and fever from viral infections such as enteroviruses are common, especially in children, and most people recover. We don’t know why a small number of patients develop AFM, while most others recover. We are investigating possible:
- Direct infection of a virus on the motor neurons (nerves that make the muscles move)
- Indirect infection where a virus may lead to an inflammatory or immune response directed toward motor neurons
- Host genetic factors in which certain children may be more susceptible than others
- 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 what association it may have with AFM.
- The large number of AFM cases identified in 2014 coincided with a national outbreak of severe respiratory illness among people caused by EV-D68. CDC is working with national partners to understand the annual circulation of enteroviruses, including EV-D68, and what association it may have with AFM.
- Enteroviruses most commonly cause mild illness. They can also cause neurologic illness, such as meningitis, encephalitis, and acute flaccid limb weakness, but these are rare.
So far in 2018, there are 158 confirmed cases of AFM in 36 states. These 158 confirmed cases are among the total of 311 reports that CDC received of patients under investigation (PUIs). CDC and state and local health departments are still investigating some of these PUIs.
- In 2017, CDC received information for 35 confirmed cases of AFM in 16 states.
- In 2016, CDC received information for 149 confirmed cases of AFM in 39 states and DC.
- In 2015, CDC received information for 22 confirmed cases of AFM in 17 states.
- From August to December 2014, CDC received information for 120 people confirmed cases of AFM in 34 states.
The case counts represent only those cases for which information has been sent to and confirmed by CDC.
State Case Counts
|State||AFM confirmed cases|
|New York State||2|
|New York City||3|
For more information, see
- Page last reviewed: December 10, 2018
- Page last updated: December 10, 2018
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