The Centers for Disease Control and Prevention issued a warning about acute flaccid myelitis, a polio-like illness that affects mostly children.

CDC Director Robert Redfield said in a teleconference that AFM is a public health priority.

Redfield says AFM began being monitored six years ago. The last outbreak in 2018 was the largest on record, with 238 cases in 42 states. Those cases were mostly young children - 5 years old on average.

A national outbreak has happened every other year between August and November since AFM got on the CDC's radar.

AFM's primary cause is enteroviruses, which cause the same symptoms as the common cold. Though rare, people with AFM can have sudden arm and leg weakness as well as neck or back pain. The condition progresses quickly and can lead to patients becoming paralyzed over the course of hours or days.

"Timing is critical for AFM," said Redfield "Delays in AFM recognition and care can put patients at risk."

It's unknown why certain kids develop AFM and others do not, and it's unclear how to prevent AFM. But the CDC recommends keeping up with standard hygiene - such as hand-washing.

The CDC says AFM is a medical emergency requiring immediate medical care and monitoring, and officials urge parents to not be afraid to visit the doctor during the pandemic.