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KANSAS CITY, Mo. — A polio-like condition that struck dozens of kids in the U.S. two years ago appears to be making a comeback this year. It’s still a mystery as to what exactly causes it.

Billy Sticklen was one of three kids treated at Children’s Mercy Hospital in 2014 for acute flaccid myelitis or AFM, a sudden onset of limb weakness that’s similar to polio. Billy was one of 120 kids nationwide stricken that year.

This year, there have been 32 documented cases in the U.S. through July. That’s already above last year’s total. There have been no cases in Kansas City so far, but doctors at Children’s Mercy are monitoring it.

“What we don’t know is what’s causing this uptick of AFM cases. There’s a number of viruses that have historically been known to cause this polio-like illness, and we don’t know the relationship between what’s circulating now and whether this is the cause of AFM,” said Dr. Jennifer Schuster, an infectious disease specialist.

In 2014, AFM struck during an outbreak of enterovirus-D68. The respiratory infection hospitalized hundreds at Children’s Mercy and thousands nationwide. But Dr. Schuster said a direct link between AFM and that virus has not been proven.

Children’s Mercy is seeing an increase in respiratory infections including enterovirus-D68, but the doctor says it’s an expected rise for this time of year.

“Not nearly as high as we were seeing in 2014…It’s your common cold. Some kids have runny noses, never seek medical care at all, do absolutely fine,” she said.

Others, especially those with asthma, can need acute medical care.

Dr. Schuster said to prevent those infections, and potentially cases of AFM, wash your hands frequently and stay home from school or work when you’re sick.

Billy Sticklen regained movement in the months after the polio-like condition struck him, but some children have not.

Parents should, of course, seek immediate medical help if there’s a sudden onset of limb weakness in your child. Some, but not all, of the kids with AFM reported having respiratory or stomach illnesses before the weakness hit them.