Skip to main content

KingCounty.gov is an official government website.

Official government websites use .gov
Website addresses ending in .gov belong to official government organizations in the United States.
Secure .gov websites use HTTPS
A lock or https:// means you've safely connected to the .gov website. Only share sensitive information on official, secure websites.
King County Washington home

October 19, 2026

Watch for potential cases of Acute Flaccid Myelitis

➜ This health advisory is also available in PDF format (215 KB)

Current situation

Acute Flaccid Myelitis (AFM) is a rare but serious acute-onset paralytic disease, which presents with symptoms like poliomyelitis. AFM occurs in patients of any age but mainly affects children.

In 2026, the Centers for Disease Control and Prevention (CDC) is reporting at least 11 confirmed cases of AFM. In previous years, cases have been associated with increased circulation of Enterovirus D-68 (EV-D68). While no cases of AFM have been identified in Washington state this year, wastewater monitoring has indicated increased circulation of EV-D68 in recent weeks in neighboring Snohomish County and in the Western US region.

Actions requested

  1. Identify

    • Suspect AFM in patients of ANY age who present with:
      • Acute onset of flaccid weakness in one or more limbs, AND
      • MRI showing gray matter lesions spanning one or more spinal segments.
    • Consider polio in the differential diagnosis, especially in patients who are not vaccinated for polio and had recent travel to areas with high risk for polio.
    • Refer to CDC’s Evaluating Proximal Muscle Weakness to aid in your workup for AFM.

  2. Test

    • Specimens: Collect CSF, whole stool, respiratory, and serum specimens as soon as possible after onset of limb weakness.
    • Refer to CDC’s specimen collection guidance for AFM for additional information.

  3. Manage

  4. Notify

    Report to Public Health at 206-296-4774

    • Report suspected cases of AFM within 24 hours
    • Reports suspected cases of Polio IMMEDIATELY

Background

AFM is a rare condition that affects the spinal cord, resulting in muscle and nerve weakness similar to the clinical presentation for polio. Although AFM can occur in patients of any age, it mainly affects children. Most people with AFM have sudden onset of arm or leg weakness with loss of muscle tone and reflexes in the affected limb (or limbs). Although AFM has a variety of possible causes, it is strongly suspected that AFM is caused by a viral respiratory pathogen such as enterovirus; most AFM patients report a history of febrile illness 1–2 weeks before their onset of acute flaccid limb weakness.

Enterovirus D-68 (EV-D68) is believed to be the main enterovirus circulating in prior years with elevated cases (including 2014, 2016, and 2018). In past years, increases in EV-D68 respiratory disease have preceded cases of AFM by about 2 weeks. Although we are seeing increases in EV-D68 detections in the United States this year, the number of reported cases of AFM has remained relatively low to date. As of October 2, 2026, CDC has received 26 reports of suspected AFM, with 11 confirmed cases in 9 states. Increases of reported AFM cases occurred in 2016 and 2018, with 10 and 11 cases reported in Washington, respectively. Since 2019, sporadic cases of AFM have been reported in Washington.

The identification of a paralytic polio case in an unvaccinated person in New York in 2022 reinforced the need to also consider polio in the differential diagnosis of patients with sudden onset of limb weakness. Clinicians should obtain whole stool samples from all patients with suspected AFM to rule out poliovirus infection. This is particularly important if the patient is under-vaccinated or unvaccinated against polio, and if the patient has a history of recent travel to an area at high risk for polio.

Resources

AFM resources

Polio resources