The puzzling condition, known as Acute Flaccid Myelitis, causes partial paralysis in children and bears a striking resemblance to polio.
The Washington Department of Heath says all the children are 6 or younger. Among them is two-year-old Julia Payne, whose symptoms started off resembling those of a common cold.
The first five possible cases affected children in King, Pierce, Lewis and Snohomish counties.
It's not a new condition, but the Centers for Disease Control and Prevention says the increase is not normal.
The CDC began tracking the cases in 2014 after seeing an uptick in the number of cases.
The agency said it hasn't confirmed the cause for the majority of the cases, which primarily occur in children. "And only about five cases have been reported", Hicar said.
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AFM has been reported in 26 states in the US, with a total of 85 cases and climbing.
OR hasn't had any cases of AFM this year.
In September, the Illinois Department of Public Health sent out an alert to health providers about AFM.
In 2014, 120 children were diagnosed with AFM.
Earlier this week, six children in Minnesota were diagnosed with this "rare" disease. AFM can cause a range of types and severity of symptoms, but the commonality among them is a loss of strength or movement in one or more arms or legs.
Other causes have been linked to environmental toxins, genetic disorders and viruses similar to the West Nile virus, according to state health officials. The cause of any individual case of AFM can be hard to determine, and often, no cause is found. CDC specialists will make the final determination if these cases are AFM. Staying update on recommended immunizations is also important to avoiding vaccine preventable illnesses.