Update on Acute Flaccid Myelitis in the US: Cases Continue to Rise

Image courtesy of Eric Fischer on Flickr, CC

According to the US Centers for Disease Control and Prevention (CDC), there have been 158 confirmed cases of acute flaccid myelitis (AFM) in 2018, with 311 cases currently being investigated [1]. AFM is a rare condition that affects the nervous system, causing weakness or paralysis in at least one limb [2]. Cases have been confirmed in 36 states, with the highest numbers in Texas (21 cases) and Colorado (15 cases) [1]. Most of the cases have occurred in children, with a median age of four years (range= 7 months to 32 years) [3]. There have been no AFM-associated fatalities in 2018 [4].

In most patients with AFM, the earliest symptoms include a fever and respiratory symptoms [5]. More than 90% of the confirmed cases in 2018 had viral symptoms before any paralysis developed [1]. Sudden onset of paralysis typically occurs three to 10 days after the initial symptoms [5]. AFM patients may experience sudden weakness in their arms and/or legs, a loss of muscle tone, and decreased or absent reflexes [6]. If the nerves controlling the head and neck are affected, the patient may experience facial weakness, drooping eyelids, and difficulty swallowing or speaking. Respiratory failure may also occur. About half of the cases will fully recover, while the others may experience permanent disabilities [5].

The cause of AFM is currently unknown. Despite symptoms resembling those of polio, there is no evidence that AFM is caused by poliovirus [1]. However, some of the possible causes under consideration include enteroviruses (of which poliovirus belongs), rhinoviruses, or an overreaction of the immune system [5]. Of the 440 cases that have been confirmed since 2014, coxsackievirus A16, Enterovirus-A71 and Enterovirus-D68 have been detected in the spinal fluid of only four cases [1].

Most cases of AFM develop between August and October, with increased case counts occurring every other year [1,2]. The annual AFM confirmed case counts between 2014 and 2018 are as follows [1]:

  • In 2014, there were 120 confirmed cases in 34 states
  • In 2015, there were 22 confirmed cases in 17 states
  • In 2016, there were 149 confirmed cases in 39 states and DC
  • In 2017, there were 33 confirmed cases in 16 states

In 2014, the increased number of cases of AFM coincided with a national outbreak of EV-D68, but no large outbreaks of respiratory illness were observed in 2016, when case counts of AFM were also elevated [3].

There is currently no specific treatment for AFM [7]. Physical and occupational therapy are often used to help with limb weakness. A few other therapies have also been considered, including corticosteroids, intravenous immunoglobulin, plasmapheresis, and antiviral medication, but there is currently not enough evidence to suggest these treatments are effective for AFM [8].

On November 19th, CDC Director Robert R. Redfield, M.D. announced that the CDC has established an Acute Flaccid Myelitis (AFM) Task Force to help investigate the cause and treatment of AFM [9]. In his announcement, Dr. Redfield said, “This Task Force will ensure that the full capacity of the scientific community is engaged and working together to provide important answers and solutions to actively detect, more effectively treat, and ultimately prevent AFM and its consequences” [9]. The task force delivered its first report at the CDC’s Office of Infectious Diseases Board of Scientific Counselors’ public meeting on December 6, 2018.


  1. https://www.cdc.gov/acute-flaccid-myelitis/afm-surveillance.html
  2. https://www.reuters.com/article/us-cdc-acuteflaccidmyelitis/cases-of-rar…
  3. https://www.cdc.gov/mmwr/volumes/67/wr/pdfs/mm6745e1-H.pdf
  4. https://www.cbsnews.com/news/cases-of-mystery-illness-causing-paralysis-…
  5. https://www.npr.org/sections/health-shots/2018/11/13/667377572/mysteriou…
  6. https://rarediseases.info.nih.gov/diseases/13142/acute-flaccid-myelitis
  7. https://www.cdc.gov/acute-flaccid-myelitis/downloads/fs-acute-flaccid-my…
  8. https://www.cdc.gov/acute-flaccid-myelitis/hcp/clinical-management.html
  9. https://www.cdc.gov/media/releases/2018/p1119-cdc-establishes-afm-task-f…

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