In August of 2014 the CDC began tracking a sudden increase in Acute Flaccid Myelitis (AFM) cases which were tentatively linked to EV-D68 - a relatively rare non-polio enterovirus - that at the time was causing a nationwide outbreak of mild to moderate respiratory, mostly among children and teenagers.
Acute flaccid myelitis (AFM) is a rare illness that affects a person’s nervous system, specifically the spinal cord. AFM falls under a broader `umbrella' of syndromes called Acute Flaccid paralysis (AFP). AFM may be due to a variety of causes, including viral infection.
The number of AFM cases dropped by nearly 80% in 2015 (see chart above), but has once again spiked in 2016 - and this time without a concurrent EV-D68 outbreak spreading across the nation.
While a circumstantial case has been posited to link AFM to EV-D68 over the past couple of years (see EID Journal Enterovirus D68 Infection in Children with Acute Flaccid Myelitis, Colorado, USA, 2014), no definitive causal link has been established.
There are many other viruses - including EV-71, West Nile Virus, cytomegalovirus and Epstein-Barr virus, along with some of the adenoviruses - that are known to cause similar neurological symptoms.
All of which leaves us with a medical mystery as to what is causing this resurgence of AFM, one that equaled by the end of last November, the 120 cases reported in 2014.
This January update from the CDC.
AFM in the United States
At a Glance
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.
- 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 November 2016, 120 people in 37 states were confirmed to have 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.
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 November 30, 2016, a total of 120 people in 37 states across the country were confirmed to have AFM.
Updated January 2, 2017
^ Cases reported as of December 31, 2016 with onset of illness through November 30, 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 a revised 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.
What This Graph Shows
- From January 1 to November 30, 2016, 120 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 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 December 31, 2016 with onset of illness through November 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.
What we know about the AFM cases reported since August 2014:
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 there were no cases of EV-D68 detected and so far in 2016, only limited sporadic cases of EV-D68 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 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.
(Continue . . . )
You can access earlier updates on the following blogs: