In AFM, the gray matter of the spinal cord gets damaged, leading to muscle weakness and paralysis.
The Centers for Disease Control and Prevention says there are now 62 cases across 22 states this year.
At the press conference, Messonnier emphasized how rare the disease is.
Follow-up with patients from the 2014 and 2016 waves has shown that most children do not recover from acute flaccid myelitis, for which there now is no cure.
Symptoms of AFM are similar to polio.
There is no known cause or treatment, a state Department of Public Health advisory said. They say they are investigating several potential causes, including environmental toxins.
"We are seeing more cases of this in the USA than we are seeing in polio in the whole world", University of Colorado neurologist Kenneth Tyler tells Science. "Right now, we know that poliovirus is not the cause of these AFM cases".
While AFM is not unique to the US, Messonnier said, "no one else has seen seasonal clustering every other year". "You can't tie it up in a neat bow". For example, 11 of the Colorado cases of AFM this year have tested positive for EV A71, a rare type of enterovirus not usually seen in the U.S., rather in Asia and other parts of the world, according to state epidemiologist Dr. Rachel Herlihy.
AFM was first detected in 2014, when 120 cases were confirmed.
More than 90 percent of cases are in children. That makes 2018 look like it might end up being a year with more cases than usual, the CDC's Dr. Nancy Messonnier told reporters. A spokeswoman for hospital said they have notified the health department and are working with the CDC to learn more about the illness. One child died from AFM in 2017.
Right now, it's unclear what has caused the AFM cases in Illinois, Colorado, and Pittsburgh. Enterovirus (EV) D68, a virus from the same family as polio, is the leading suspect, having been closely linked to the 2014 outbreak, Pardo-Villamizar said.
The agency doesn't know who may be at higher risk for developing this condition or the reasons they may be at higher risk. But the kids don't go to the same school, nor are they located near each other.
Rathore, the Jacksonville specialist, said he was not shocked at seeing a case this year. She said the cases were definitely not caused by the polio virus, which has not been found in any of the stool samples from affected children.
There is no specific treatment for the virus.
The long-term effects of the disease are also unknown.
The outlook for patients with AFM can vary from a quick recovery to ongoing paralysis, Messonnier said. "Parents need to know that AFM is very rare, even with the increase in cases that we are seeing now".
One thing scientists do know is that only one person in a million is infected with AFM each year in the United States.
"As a parent myself, I understand what it is like to be scared for your child".
It's still not clear what is causing the condition, which can develop after a viral infection.
Ehresmann also noted that now that school is in session and cold weather months are coming, it's more crucial than ever that people maintain strict hygiene habits. "You don't need an very bad lot of paralyzed children to make this an important problem".