The US Centers for Disease Control and Prevention, which releases only confirmed numbers, says 16 states had 38 cases as of September 30.
Other states with cases included Colorado, Illinois and Washington.
"Parents need to remain vigilant for signs of muscular weakness or difficulty breathing that develop during and after recovery from an upper respiratory infection", Glatter said.
This summer the Oklahoma State Department of Health referred a case to the Centers for Disease Control and Prevention. "For some of the previous cases we've identified one pathogen or another, but we have no unifying diagnosis". Some patients have tested positive for enterovirus or rhinovirus. Polio was eradicated in the U.S.by vaccination.
The disease affects the body's nervous system and can cause paralysis. "It's an outbreak of a disease with known symptoms and complications but unknown causes or routes of transmission".
Media reports in recent weeks have suggested that a "polio-like virus" might be triggering the condition, elevating fears that it might be polio itself. But she stressed that despite the increase in cases, the illness is still very rare, occurring in fewer than 1 in a million people in the US each year. That pattern appears to be repeating this year.
Since officials have been unable so far to determine how the disease spreads, they are starting to count suspected cases as well as confirmed to better anticipate increases over the coming months.
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The CDC is investigating 127 reported cases, including the ones that have been confirmed.
Depending on which part of the spine is damaged, different muscles can become weak or paralyzed.
"If we knew what causes it, we could treat it", said Dr. Mobeen Rathore, chief of infectious diseases at Wolfson Children's Hospital. "Ninety percent of the cases are in those less of 18 years in age", Messionnier told NBC News.
But, if their child is diagnosed, parents should prepare for extensive physical therapy - therapy that isn't always covered by insurance, he said. Limb paralysis caused by the illness can worsen quickly, so it's also important that individuals experiencing these symptoms receive prompt medical attention.
The disease, that has no specific treatment of vaccine, remains rare, affecting one in a million. It's also a serious condition. AFM symptoms include sudden muscle weakness in the arms or legs, sometimes following a respiratory illness.
It advised that if one's child has similar symptoms, seek medical care right away.
"This is actually a pretty dramatic disease", she said. "These kids generally have a sudden onset of weakness", Messonnier said.