At least 62 cases have been confirmed in 22 states this year, and at least 65 additional illnesses in those states are being investigated, according to the Centers for Disease Control and Prevention (CDC).
Between August 2014 and September 2018, 362 cases were confirmed by the CDC.
Experts say the early symptoms of the disease include arm or leg weakness, and loss of muscle tone.
Acute flaccid myelitis is not a virus. Testing of affected children has turned up a smattering of infections - some by enteroviruses, which is the broad family to which polioviruses belong, but also rhinoviruses, which cause head colds.
"But these kinds of things are more hard", said Pastore y Piontti of the reports of the new outbreak.
And even if a case can be narrowed down to a virus, there are multiple kinds of viruses it could be. "This is likely a rare complication from a common virus". He is an assistant professor and child neurologist at the Stanford University School of Medicine.
A mystery illness paralyzing children, is spreading across the country.
The CDC says that there has been an increase in cases of AFM since 2014.
The CDC says AFM's cause can vary from a virus to environmental toxins to genetic disorders.More news: Rise in hate crimes with 52 % of religious offences against Muslims
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"There is a lot we don't know about AFM", Messonnier said during a teleconference for reporters.
Acute flaccid myelitis typically causes weakness in the arms and legs, but can affect other muscle groups.
While the CDC has yet to confirm a case in Virginia, Hoff said her son Camdyn was diagnosed with AFM while hospitalized at UVA Medical Center, falling ill with the telltale symptoms.
Many local cases have been treated at Children's Hospital of Philadelphia.
On a Facebook page dedicated to the disease, one parent posted that her daughter was diagnosed with AFM four years ago after catching enterovirus. The study was published in the journal Developmental Medicine and Child Neurology.
As with any illness, parents should take their child into a doctor for treatment. There have been cases each year since, but the numbers have been higher on alternate years. AFM may be one of them.
There is no specific treatment for the virus.
"There's better recovery this year in the kids we're seeing here with EV A71", Dominguez said, as opposed to EV D68.
It's still not clear what is causing the condition, which can develop after a viral infection.
"It's rare, but certainly when you hear about it it's very scary for parents", CBS News medical contributor Dr. Tara Narula told "CBS This Morning". "So I think that should be reassuring to people", Dominguez said. It's only a small handful of children who progress to the muscle weakness associated with AFM. Polio, while once widespread, has been largely eradicated due to the polio vaccine.
"Good advice now is good advice going into the influenza season", Dominguez said.