"We know this can be frightening for parents, and I know many parents want to know what signs and symptoms they should be looking out for in their children," she said. Parents should seek medical care immediately if their child develops sudden weakness or loss of muscle tone in the arms and legs.
Some patients diagnosed with this condition have recovered quickly but others continue to have paralysis and require ongoing care, she said.
The CDC began tracking the condition in 2014, when there were 120 confirmed cases. Then in 2016, there were 149 confirmed cases. Officials said it's too early to know whether the total cases for 2018 will surpass those previous years. But the data reported Tuesday represents "a substantially larger number than in previous months this year," Messonnier said.
Parents and clinicians should remember that this is a rare condition, affecting less than one in a million people, she said. "As a parent myself, I understand what it's like to be scared for your child," she said. "Parents need to know that AFM is rare even with the increase in cases we are seeing now."
Still, because this is a "pretty dramatic disease," Messonnier said, health officials want to raise awareness about the symptoms to ensure parents seek medical care immediately if their children show a sudden onset of weakness in their arms and legs.
The agency knows that poliovirus is not the cause of these cases because the CDC has tested every single stool specimen from patients and none have tested positive for poliovirus. Messonnier said West Nile virus, which had been listed as a possible cause on the CDC's website, is not causing the illnesses.
In some individuals, health officials have determined that the condition was from infection with a type of virus that causes severe respiratory illness.
But the agency doesn't know who may be at higher risk nor why they may be at higher risk. CDC has tested many different specimens from patients with this condition for a wide range of pathogens, or germs, that can cause AFM. But so far, no pathogen has been consistently detected in the patients' spinal fluid.
Parents can best protect their children from serious diseases by taking prevention steps, like washing their hands, staying up to date on recommended vaccines, and using insect repellent to prevent mosquito bites, she said.
There is no specific treatment for AFM, but neurologists who specialize in treating brain and spinal cord illnesses may recommend certain interventions, such as physical or occupational therapy, on a case-by-case basis.
The CDC is not releasing a list of the 22 states with confirmed and suspected cases because of privacy issues. But some state health departments, such as Minnesota's, have reported the numbers.
States are not required to provide this information to the CDC but have been voluntarily reporting their data. Working with local and state health departments and hospitals, the CDC has been able to confirm a number of these cases faster, she said.