The federal Centers for Disease Control and Prevention is investigating 127 cases of possible AFM, including 62 that have been confirmed in 22 states this year.
The increase in cases has been happening since 2014, usually in August and September, but only in 2014 and 2016, Messonnier said in a news briefing with reporters.
CNN has reported that this year, more than half of all USA states have had confirmed or possible cases, including North and SC.
In 2014, a large AFM epidemic coincided with a national outbreak of severe respiratory illness caused by enterovirus D68 (EV-D68), but in-depth testing of patient samples hasn't consistently found a common cause.
According to yesterday's warning issued by the CDC, the disease could be linked to environmental toxins, genetic disorders or other viruses such as West Nile.
Some victims have been infected with viruses, but researchers have been unable to identify a single virus responsible for all cases.
Acute flaccid myelitis, also called AFM, is a rare but serious condition that affects the nervous system and causes the muscles and reflexes to suddenly become weak, she said Tuesday. Symptoms include muscle weakness, droopy eyelids, problems swallowing, and slurred speech. Only one death has been reported, which involved an AFM illness reported in 2017.
Carlos Pardo-Villamizar, a neurologist and director of the Johns Hopkins Transverse Myelitis Center, said that the mystery lies in whether the damage seen in AFM is caused by an external agent or the body's own defenses.
A study published last year found 6 of 8 children in Colorado with acute flaccid myelitis still struggled with motor skills one year after their diagnosis. Officials have been baffled by the increase, and are starting to count suspected cases as well as confirmed ones to better anticipate increases in confirmed cases over the coming months.
She said that CDC has tested every stool specimen from AFM patients. The public health agency also does not fully understand long-term consequences or why some patients recover quickly while others continue to experience weakness.
Messonnier stressed that while she understands how frightening this situation is for parents, they should remember that the infections are, in fact, rare.
About 120 confirmed cases were reported in 2014.
That's up from 22 people who were said to have it in 2015. Health officials are alarmed and frustrated, because a specific cause hasn't been identified. Officials said it's too early to know whether the total for 2018 will surpass those previous years.
The CDC is investigating the cases and monitoring the disease, and encourages people to prevent the disease by staying up to date on vaccines, washing hands and protecting against mosquito bites.
States are not required to provide this information to the CDC but have been voluntarily reporting their data.
The CDC referred calls to individual state health departments.