The polio-like illness causes limited mobility or paralysis.
Dozens of children across the United States have developed a rare polio-like illness, but the reason for this spike in cases remains a mystery, according to health officials.
The agency also said it will post case count updates on its website every week now, a change from the monthly updates it had been giving. "We want to encourage parents to seek medical care right away if you or your child develops symptoms of AFM, such as sudden weakness and loss of muscle tone in your arms or legs".
The CDC says the illness could be caused by viruses, environmental toxins, genetic disorders, or a condition in which the immune system attacks body tissues. 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.
Doctors say that most of the reported cases of AFM involve those under the age of 18.
According to the Douglas County Health Department, a suspected case of AFM is being investigated in a young child.
Once diagnosed, some patients have recovered quickly, but some continue to have paralysis and require ongoing care, Messonnier said. Officials would not say what states they lived in, but cases have been reported in New York, Minnesota, Illinois, Colorado, and Washington. "We actually don't know what's causing this increase", said Dr. Nancy Messonnier, of the CDC. Officials said it's too early to know whether the total cases for 2018 will surpass those previous years.
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The CDC received information on 33 confirmed cases of AFM across 16 states in 2017, 149 cases in 39 states.
After testing patients' stool specimens, the CDC determined poliovirus is not the cause of the AFM cases.
"This is a pretty dramatic disease", Messonnier said.
Messonnier said the CDC has definitively ruled out polio - which causes a similar set of symptoms - as the cause.
Parents have reported that the limbs of affected children appear lifeless.
All of the worries about AFM just give parents and grandparents one more thing to worry about. In the CDC's health warning the organisation said at least 65 other patients are being assessed after they displayed symptoms of the malady.
But Messonnier said that, in general, parents can help protect their children from diseases by washing their hands, making sure their children are up to date with vaccinations and applying insect repellent to protect against mosquito bites, which can spread viruses.