By Stephanie Stahl

PHILADELPHIA (CBS) — The mysterious condition that causes polio-like symptoms in children has arrived early in Pennsylvania as federal health officials issued a warning Tuesday to parents and doctors to be watchful. The illness usually arrives in August, but there are already 11 cases nationwide, including one in Pennsylvania.

Health officials say it’s a rare but serious condition that’s contagious and can strike anyone, anywhere.

Scarlett Camburn, of Havertown, is among the children who had serious complications from acute flaccid myelitis, which is also known as AFM.

It’s a rare polio-like condition that affects the spinal cord. AFM is caused by a virus that usually strikes children in the late summer or early fall.

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The Penn Health Department says there is already one confirmed case in 2019 and one that is suspected.

The Centers for Disease Control and Prevention is now warning parents and doctors to be on the lookout.

“We really need to be aware that we’re coming into enterovirus season,” Dr. Sarah Hopkins, from the Children’s Hospital of Philadelphia, said.

Hopkins is helping the CDC investigate the mysterious condition, which is tricky to diagnose.

Symptoms include sudden onset of arm or leg weakness, difficulty moving facial muscles along, slurred speech and trouble swallowing.

Most children are sick with a respiratory virus before AFM develops.

“It’s important to seek care early,” Hopkins said.

Hopkins says there’s been a new, significant advance with the identification of an enterovirus linked to most cases.

“Similar in some ways to a cold virus that’s transmitted by respiratory secretion,” she said. “For some reason some people are more susceptible to having the virus cause problems in their spinal cord.”

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There have been outbreaks of AFM in 2014, 2016, and 2018, which was the largest outbreak.

Last year, there were 233 confirmed cases in 41 states, including 11 in Pennsylvania. There were also 26 additional probable cases and two deaths.

It’s unclear why AFM strikes mainly in warm weather. Hopkins says most children who get the virus do not develop the condition, but if they develop weakness in the arms or legs, they should be evaluated by a doctor.

Stephanie Stahl