A Mysterious Illness Hits Record Number of Cases: The CDC Is Urging Action

"The 2018 outbreak was the largest so far."

Acute flaccid myelitis is rare, but for children who contract the illness, it’s serious. And on Tuesday, the CDC announced that it’s become more common.

Known as AFM, the disease affects the spinal cord, causing limb weakness and sometimes even partial paralysis. These symptoms have drawn comparisons to polio. Experts say it’s not polio, but even as more evidence is gathered, an exact cause of AFM has still not been identified.

And the situation seems to be worsening, the US Centers for Disease Control and Prevention announced Tuesday.

In its Vital Signs report, CDC officials announced that the number of AFM cases in 2018 was the highest it’s been since the CDC started tracking it in 2014. In 2014, there were 120 confirmed cases in 34 states. In 2018, that number rose to 233 cases in 41 states.

“There have been three nationwide outbreaks of AFM starting in 2014 when CDC started tracking this illness,” CDC Principal Deputy Director Anne Schuchat, M.D., told reporters Tuesday.

The average age of patients is five years old, and there’s no clear bacterium, virus, or toxin causing it — and therefore no cure and no vaccine. In the search for a culprit, one of the most notable pieces of evidence is when the illness shows up.

“We’ve seen a seasonal pattern to this illness,” said Schuchat. “Most patients develop AFM between August and October. Most patients had a mild respiratory illness or fever less than a week before they developed arm or leg weakness. There are important pieces of evidence that point to viruses, including enteroviruses in particular, playing a role in AFM.”

One of these pieces of evidence is the biennial pattern, with cases spiking on even-numbered years, and dipping during odd-numbered years — a trend that experts say points to viruses.

Acute flaccid myelitis is increasingly common, but it's still quite rare. Doctors are struggling to identify its cause.


All specimens collected from suspected AFM patients tested negative for polio, but about half were positive for enteroviruses and rhinovirus (the common cold). Out of 74 patients from whom doctors collected samples of cerebrospinal fluid, only two tested positive for the enteroviruses EV-A71 and EV-D68.

Doctors suspect that AFM is the body’s response to an infection, even if the infection isn’t “causing” the illness per se, and they hope that further research will illuminate the connection between these viral infections and the limb weakness and paralysis that follows.

“When a virus is found in the spinal fluid, it’s good evidence that this was the cause of the patient’s illness,” Tom Clark, M.D., M.P.H., the deputy director of the CDC’s Division of Viral Diseases, told reporters.

Since cases were reported to the CDC between 18 and 36 days after symptoms began, it’s possible that patients’ bodies cleared the culprit viruses before any samples were collected.

“This delay hampers our ability to understand the causes of AFM,” Clark said.

CDC graphic on identifying AFM


For this reason, Schuchat urged doctors to report cases as soon as possible and collect samples as when they have a patient show up with limb weakness.

Not only will early reporting help the CDC track cases of AFM, it will also allow the CDC to collect specimens from patients to help investigate the commonalities among patients and get closer to identifying the root cause of the illness.

As CDC doctors focus on nailing down the cause of AFM, the long-term consequences stay with patients. While most patients have recovered the use of their limbs, Lydia Marcus, M.D., a pediatric neurologist who’s been investigating AFM, previously told Inverse that none of her AFM patients had fully recovered limb strength.

As part of the CDC’s monitoring efforts, Schuchat said they will be returning to patients over time to track their recovery.

“We’ll learn a lot more about the persistence of limb weakness after AFM,” she said.

“The 2018 outbreak was the largest so far with 233,” Schuchat added. “Does that mean 2019 or 2020 will be even bigger? We really can’t say. … It’s too early in the course of this condition for us to understand what will happen in the future.”

For now, the focus is on learning as much as possible about the illness so that eventually doctors can develop cures. In the meantime, the CDC recommends taking the same precautions you would take with any communicable disease: Wash your hands.

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