-- Eight children in Washington state have been confirmed with cases of a rare syndrome that can result in paralysis -- and health officials are searching for answers.
But the reason the children developed the condition has remained a mystery. Federal and state health officials continue investigating why these eight children developed the debilitating syndrome -- acute flaccid myelitis (AFM) -- that affects the nervous system.
Historically, the syndrome has been caused by a variety of infections, including the polio virus. The illness often causes the spinal cord to be inflamed, which can, in turn, cause temporary or permanent paralysis.
The eight known cases of AFM were reported last week by the Washington State Health Department, which continues to investigate the cluster along with the U.S. Centers for Disease Control and Prevention (CDC).
"We haven't found evidence to identify what's causing these cases," a CDC spokesman told ABC News today, "but this investigation is ongoing. We are continuing to work with Washington to examine case reports for potential causes and risk factors as well as providing technical assistance and communication support."
The children in the confirmed cases range in age from 3 to 14 years old and were identified in five different counties in Washington state.
All of the children had weakness or loss of movement in one or more limb, according to the state health department. The syndrome is known to cause varying degrees of paralysis.
Three of the sickened children remain hospitalized and five have been released. One child, who died after developing neurological symptoms, was found not to have AFM.
When a cluster of cases is confirmed, health experts will quickly examine samples to see if all of the affected patients have been infected with a common virus, Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center told ABC News.
"They'll say 'OK, they're all AFM and they're grouped geographically and roughly in time,'" Schaffner said.
"At that point, they start to look for all the causes," he explained, "they get the clinical specimens ... get blood and stool and cerebral spinal fluid."
Many viruses that cause AFM, including the polio virus, can be identified through tests. But it has been difficult in past outbreaks to identify the viruses in sick patients, Schaffner said.
In 2014, the CDC suspected that an outbreak of respiratory virus called enterovirus D68 might have led to an increase in AFM cases. However, as they investigated, they could "not consistently detect a pathogen" in the affected patients' spinal fluid. They were not able to point to the virus as a cause in those AFM cases.
Another complication when looking for a root cause in AFM outbreaks is that it can be an immune system response to an infection that has already passed.
"That would be a question that would be asked, 'Is this more an illness like Guillian Barre syndrome or is this more like polio myelisitis [polio-caused spinal inflammation] where it gets in the spinal cord and destroys nerve cells?" said Schaffner.
"They're trying to keep an open mind," he said.
Infection control procedure is important in any viral-related illness, even when the specific source of the infection is not known.
At Seattle Children's Hospital, where all the children in the Washington State outbreak have been treated, officials said they are taking steps to keep possible infections from spreading.
"Patient safety is our top priority at Seattle Children’s, and parents should know that it is safe to bring their children to the hospital," Dr. Mark Del Beccaro, chief medical officer at Seattle Children’s Hospital said in a statement Friday. "We are using appropriate standard infection control, including putting patients with symptoms of active respiratory infections in isolation so they do not have contact with any other patients."