The Centers for Disease Control and Prevention is warning of a possible outbreak of a new polio-like disease called Acute Flaccid Myelitis or AFM.
It starts with flu or strep-like symptoms, but according to doctors, it can quickly attack the spinal cord, causing paralysis in the arms and legs, facial drooping and trouble swallowing.
So far this year, there have been at least 62 confirmed cases in 22 states – most of them children. The average age is just four years old. Another 65 additional illnesses in those affected states are being investigated as possible incidents of AFM.
"It's different from anything else I've come across in my career," says Dr. Fernando Acosta, Jr.
Clusters of the mysterious illness have occurred in Minnesota, Illinois, Colorado, New York and Washington.
Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the CDC, said, "Despite lots of investigation by CDC and its partners, we don't know where AFM comes from and we don't know what's causing it."
About 90 percent of the cases are children who have suffered muscle weakness or paralysis, including in the face, neck, back or limbs. The symptoms tend to occur about a week after they had a fever and respiratory illness.
Oddly, this illness appears to spike in the US every two years – there were 120 confirmed cases in 2014 and 149 cases in 2016. Those waves of illness were partly attributed to particular strains of respiratory germs called enteroviruses.
Officials say AFM is rare, affecting about one in a million, but they're still urging parents to look for any sudden weakness in their children's arms or legs.
"This is a mystery so far," Messonnier said. She says that while it's "a pretty dramatic disease," most kids do recover.