She noted the confirmed cases are in 22 states.
Officials at Children's Mercy Hospital in Kansas City said two cases of AFM have been confirmed at the hospital.
It's a debilitating, mystery illness.and it's spreading.
When AFM strikes, patients experience sudden weakness, as well as loss of muscle tone and reflexes in the arms and legs.
"A polio-like disease because in the sense that it does involve the same areas in the nervous system", said Dr. Cristina L. Sadowsky, clinical director for the International Center for Spinal Cord Injury, with Kennedy Krieger Institute. The most severe symptom of AFM is respiratory failure, which can happen when the muscles needed to breathe become weak from the disease. Since the phenomenon began in 2014, she said, the rate of infections has been less than one case per 1 million children in the country.
The agency had a teleconference with health providers slated for later today, and it provided a toolkit for diagnosing AFM, along with instructions for reporting suspected cases.
So far the disease has claimed one life in the U.S.
Federal health officials released the updated numbers on Tuesday, and said they still had no idea what was causing the spike in AFM cases or why kids were getting it in the first place.
Cases similar to Tunan's son are spreading to children around the age of four nationwide. No geographic clustering has been found and there is no other "unifying factor to explain the peaks", she added.
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The CDC says it seems to be following an every other year pattern that emerges in the fall. "We actually don't know what's causing this increase", said Dr. Nancy Messonnier, of the CDC.
Because officials don't know the cause of AFM, they can't recommend a specific way to prevent it. CDC has tested many different specimens from patients with this condition for a wide range of pathogens, or germs, that can cause AFM. Some patients have tested positive for enterovirus or rhinovirus.
The cause for the rare condition is still unclear.
More broadly, she noted, "there is a lot we don't know about AFM".
That's up from 22 people who were said to have it in 2015.
Messonnier said some patients diagnosed with AFM have recovered quickly while others continue to struggle with paralysis.
On Monday, CNN reached out to health departments in every state and received responses from 48 states plus the District of Columbia.
Officials said they will be conducting additional analysis on this year's cases.
The MDH says the case is now being reviewed, and did not provide information regarding where in the state this particular case was diagnosed, or whether or not the child is in the hospital. "There's going to be a delay, a lag in the timing of some of these reports".