The hospital is now working with the health department and Centers for Disease Control and Prevention to administer testing to confirm if the child does indeed have AFM.
Two-year-old Julia Payne is one of two children being treated for AFM in Chicago.
Dr. Fernando Acosta Jr., a neurologist at Cook Children's, said there is no cure or treatment at this time.
AFM is a rare condition that affects the nervous system, specifically the spinal cord.
"All cases are among infants and children under age 6 who all reportedly had symptoms of a respiratory illness in the week prior to developing symptoms of AFM", the Washington State Department of Health said in a statement Wednesday.
"At this point there isn't evidence that would point to a single source of illness among these cases", said Dr. Scott Lindquist, state infectious disease epidemiologist at the Department of Health.More news: China's central bank cuts reserve ratio for some lenders
More news: UFC 229: Ferguson and Pettis Must Stay Focused on Saturday Night
More news: Gov. Rick Scott warns of 'monstrous storm' with massive flooding
AFM is a weakening of the nerves that causes partial paralysis in children.
Symptoms include drooping face and eyelids, difficulty moving eyes and swallowing, and slurred speech. "We're working closely with medical providers and public health agencies".
The CDC says it got information on 362 cases of the illness in the US from August 2014 through August 2018. Until then, doctors are treating the cases as if they are AFM. "We'll continue to investigate and share information when we have it". The cause of any individual case of AFM can be hard to determine, and often, no cause is found. CDC specialists will make the final determination if these cases are AFM.
For the first nine months of this year, 38 people in 16 states have been confirmed to have AFM.
Doctors now don't know a lot about how AFM spreads. Many people compare the disease to polio because it can cause problems that are very similar to the poliovirus. Fewer than 1 in 1 million people will contract AFM, even when these new numbers are taken into account.
Experts say good hygiene and making sure little ones are washing their hands are one way to prevent spreading viruses and germs. Three cases were reported in 2017, and one other case was reported in Washington since the beginning of 2018.