Acute flaccid myelitis (AFM) — a paralytic condition in children that appeared mysteriously in 2014 — is almost certainly of viral origin and most likely an enterovirus, an investigator with the Centers for Disease Control and Prevention (CDC) recently reported.

“There is growing evidence to suggest enteroviruses as the leading etiologic agent for acute flaccid myelitis,” Susannah McKay, PhD, MPH, told Hospital Infection Control & Prevention. “Nearly all patients with AFM reported some symptoms suggestive of viral illness before developing AFM. About half of the patients with AFM who had specimens tested have evidence of an enterovirus.”

An investigator with the CDC’s Epidemic Intelligence Service (EIS), McKay spoke at press conference at the recent EIS meeting in Atlanta. AFM emerged in 2014 during a large national outbreak of Enterovirus D68 (EVD-68) and has peaked and ebbed in alternate years every fall since then. However, the CDC has not been able to ascribe most of the AFM cases to EVD-68 or any other specific enterovirus.

“We know that enterovirus infections are very common, and it is not clear why in rare instances some individuals develop AFM,” she said. “CDC is working hard to get in front of this.”

There is angst along with urgency, particularly from parents of children stricken by the syndrome.

“Very few patients with AFM had detectable virus in their spinal fluid, a finding that would confirm which pathogen is causing the problem,” McKay said.

Part of the CDC effort to solve the case is a new surveillance network to track respiratory infections caused by EVD-68 at seven sentinel hospitals.

“The surveillance system for EVD-68 is set up for acute respiratory illness,” said Stephanie Kujawski, PhD, MPH, a CDC EIS officer. “But the AFM team here at CDC is working with the surveillance sites to retrospectively and prospectively look into AFM.”

Indeed, it seems intuitive that EVD-68 is somehow linked with AFM, since the first cases coincided with the large 2014 outbreak.

“EVD-68 annual trends and circulation are not fully understood because testing in clinical settings is limited,” she said.

Kujawski and colleagues looked at 2017 and 2018 data from the seven geographically dispersed hospitals, finding a pattern that reflects in part the trends with AFM.¹ In 2017, when AFM had a down year, only two of 2,433 specimens for acute respiratory infection were caused by EVD-68. In 2018, investigators identified EVD-68 in 358 (13.9%) of 2,579 children tested. Almost half the EVD-68 detections occurred in September — which was also the peak month for AFM in 2018. The EVD-68 infections were severe, with 262 (68%) of patients requiring hospitalization.

In updating the AFM situation, McKay and colleagues reported “symptoms include limb and bulbar (neck and throat muscles) weakness, similar to poliomyelitis.”² Polio is the historic disease that casts a long shadow over AFM. Now vaccine-preventable, polio was a much-feared, crippling virus that struck children in the first half of the 20th century.

“In 2018, CDC confirmed 227 cases of AFM in 41 states,” McKay said. Overall, “94% of confirmed cases were in children less than 18 years old, with a median age of 5.”

In a subset of 175 confirmed cases, onset of AFM was preceded by a respiratory or febrile illness 95% of the time.

“For all patients who meet the clinical definition of AFM, we are asking for multiple specimens to be sent [to CDC] — not just the spinal fluid,” McKay says. “Most of the enterovirus-positive specimens that we have are from respiratory specimens.”

CDC has established an AFM task force comprised of leading experts from multiple medical disciplines to help find the cause of the paralytic syndrome and to determine prevention and treatment measures. If AFM follows its established pattern, cases will be lower this year, with an upsurge again in the fall of 2020.

“Parents and caregivers should seek medical care right away for a child who develops sudden limb weakness,” she said. “Clinicians should be vigilant for acute flaccid limb weakness, and immediately report these cases to their health department.”

For now, the generic recommendations for prevention are washing hands, avoiding contact with people who are sick, covering coughs and sneezes, and staying home when sick.

REFERENCES

1. Kujawski SA, Midgley C, Rha B, et al. Enterovirus D68 Circulation: Results from the New Vaccine Surveillance Network — United States, July–October 2017–2018. CDC EIS Conference. Atlanta, April 29–May 2, 2019.
2. McKay SL, Lee A, Lopez A, et al. Upsurge of Acute Flaccid Myelitis in the United States — CDC Surveillance Results, 2018. CDC EIS Conference. Atlanta, April 29–May 2, 2019.