SEATTLE -- Eight children from four Washington counties have received treatment at Seattle Children's Hospital for acute neurological illnesses, the state health department announced Friday.

“As part of our work to understand their symptoms, we are investigating the possibility of a condition known as acute flaccid myelitis (AFM),” the department said in a statement but added there are no confirmed cases of AFM.

Five of the children have been treated and released, but the other three remain hospitalized. Three children are from King County, two from Whatcom and Franklin counties, and one from Pierce County.

The children, whose ages ranged from three to 14, were admitted to the hospital between mid-September and Oct. 20. State officials stressed while there are similarities between the cases, the children have not received an official AFM diagnosis.

"It’s very unusual to have a cluster of these cases so close together, and I’m concerned we don’t have answers yet," said state epidemiologist Scott Lindquist.

AFM affects a person’s nervous system, specifically the spinal cord. AFM can result from a variety of causes, including viral infections, according to the CDC. Symptoms typically include sudden weakness in one or more arms or legs, loss of muscle ton, and decreased or absent reflexes.

All eight children exhibited a loss of strength or movement in one or more arms or legs.

The health department says many viruses and germs are linked to AFM, including common germs that can cause colds and sore throats, and respiratory infections. It can also be caused by poliovirus and non-polio enteroviruses, mosquito-borne viruses such as West Nile or Zika, and autoimmune conditions.

Seattle Children’s says parents should not be worried about bringing their children to the hospital.

“We are following our standard infection control protocols, including putting patients with symptoms of active respiratory infections in isolation, so they do not have contact with any other patients,” said Dr. Mark Del Beccaro, chief medical officer, in a statement.

The CDC will make the final determination regarding whether these are confirmed cases of AFM or not. There were two confirmed cases of AFM in Washington in 2014, but none last year. So far the CDC has seen 50 cases of AFM nationwide this year.