By Stephanie Stahl

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PHILADELPHIA (CBS) — There’s a growing concern about the spread of a mysterious illness that causes polio-like symptoms, mainly in children. There have been 38 confirmed cases across the country, and maybe more.

Three potential cases are being investigated in Pittsburgh as local cases in the Philadelphia area have been treated at the Children’s Hospital of Philadelphia.

For four years now, doctors at CHOP have been treating a growing number of cases. They tend to see a spike in the fall and they don’t know why. There are many unanswered questions about this virus that can strike anyone, and cause serious complications.

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Four-year-old Scarlett Camburn happily sings and plays at her home in Havertown. She’s one of the lucky ones.

She’s regaining the use of her right arm that was paralyzed by Acute Flaccid Myelitis (AFM) — a rare, but serious, illness that causes polio-like symptoms.

“We thought she was dying,” said Andrea Camburn, Scarlett’s mom.

Andrea and Christian Camburn had a perfectly healthy 2-year-old until she woke up one day and couldn’t move her arm. Spinal imaging finally confirmed that it was AFM.

“So I think it’s a very scary illness because many of these kids do have a persistent weakness to some degree,” Dr. Sarah Hopkins of CHOP said.

Hopkins says CHOP, which had two cases in August, is investigating the mysterious illness along with federal authorities. It appears the virus is spread from person to person.

“It seems to be viruses that are circulating in the community,” Hopkins said. “For instance, the bulk of these cases tend to happen between August and November.”

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

“We certainly don’t want to alarm people because it’s very rare, but at the same time, I believe it’s something that’s best to have checked out,” Hopkins said.

“It could happen to anyone and I think that’s the scariest thing,” Andrea Camburn said.

Scarlett is able to move her arm now after getting a nerve transfer operation at CHOP.

“That’s an amazing surgery,” Camburn said. “I know it’s kind of like magic.”

Scarlett’s parents have nicknamed her bad arm “Lucky” and both have “Lucky” tattoos on their arms, trying to put a happy face on a frightening ordeal.

Many children have more severe cases than Scarlett. Doctors are not sure about the exact virus or why only certain people develop the rare complications.

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There have been 38 confirmed cases of AFM across the country.

Because it spreads from person to person, doctors say good hand-washing is critical and that if children develop muscle weakness, they should see a doctor right away.

Stephanie Stahl