There have been 38 confirmed cases across the United States of a mysterious new illness called Acute Flaccid Myelitis (AFM) that causes children to exhibit polio-like symptoms.

Over the course of one week, three potential cases of this disease were brought into Children’s Hospital of Philadelphia (CHOP) to be further investigated. AFM affects the nervous system, causing symptoms like extreme weakness and paralyzation. According to an article by the University of Pittsburgh Medical Center, medical circles use the term “acute” to refer to diseases that show up suddenly, progress quickly and require urgent care.

“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,” said Dr. Sarah Hopkins to Philadelphia Local News.

CHOP, which had two cases in August, is still investigating the mysterious illness and has already asked federal authority for help. While patients may exhibit serious symptoms, this disease is not usually fatal, according to Erie News. There have been at least three cases reported in Los Angeles.

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

Doctors are not sure about the cause of the virus or why only certain people develop the rare complications. A simple treatment for Acute Flaccid Myelitis has not been developed yet, but the CDC is currently investigating possible treatments and prevention methods for AFM. Doctors recommend frequent hand washing, since the illness is passed through direct contact between people, according to the University of Pittsburgh Medical Center. Also, if a child starts to develop sudden and severe muscle weakness, they should see a doctor immediately as that is one of the most prevalent symptoms.