"Most of the cases continue to occur in children", according to its website.
The long-term effects of the disease are also unknown.
Kate Fowlie, a spokeswoman for the CDC, said in an email that many states are voluntarily reporting their data on the disease and that "many parents are coming forward to tell their stories".
The CDC has received more than 120 reports of patients under investigation for the illness this year and confirmed at least 62 cases. Outbreaks are most common from August to October, and over 90 percent of the cases have involved children under 18 years old, with the average age of those inflicted standing at just 4 years old.
Enterovirus D68 has been linked to some of the human cases of the disease, and although it is not the only cause, it has clearly been a driving force behind the three recent outbreaks, says Kevin Messacar, an infectious disease physician and researcher at Children's Hospital Colorado.
The experts emphasized that even though AFM is regularly passing through the United States, it remains a rare illness. Certain viruses that can cause AFM or similar neurologic conditions include polio, West Nile, and adenoviruses. It's only a small handful of children who progress to the muscle weakness associated with AFM.
Geography also does not appear to be a factor, with the confirmed cases spread across 22 of the 50 USA states.
The CDC has tested many different specimens from patients with this condition for a wide variety of pathogens, or germs, that can cause AFM.
"This is truly a mystery disease", Messonnier told CBS News. The highest number of cases took place in 2016, when 149 were reported cases in 39 states.
It's possible that some milder cases haven't been reported by doctors to their state health department or to the CDC, but Messonnier said she believes the number of such cases would be small, NPR reported.
"What we have been told is that he's the best case scenario of a hard situation", she said.
Parents should contact their health care provider as soon as possible if they see any symptom of AFM in their child - for example, if their child is not using his arm. He can hit them with an electric shock akin to touching a vehicle battery, he says, but they do not move.
The CDC does not know what the cause of the virus is yet.
"What is alarming and frightening is they suddenly develop weakness, and typically it's in an arm or leg. and it comes out of the blue.and that weakness comes and often times it's persists", Dr. Sanjay Gupta said. Parents who want to protect their children should encourage the same sort of good hygiene that protects kids against cold and flu, such as washing their hands frequently and covering coughs or sneezes, Dominguez said. In particular, the condition can cause weakness in the arms and legs along with loss of muscle tone and problems with reflexes.