(CNN) - The Centers for Disease Control and Prevention has confirmed 116 cases of Acute Flaccid Myelitis, also known as AFM, in 31 states.
The agency began an investigation in October after a spike in the polio-like illness, which mostly affects children.
The CDC has identified 286 possible cases in the U.S. this year.
Of those, 116 are confirmed, up by 10 from last week. That still isn’t as many as 2016, when there were 149, though the number of outstanding possible cases could eventually leave the total much higher than it has been in years.
The state with the highest number of confirmed cases is Colorado, with 15, followed by Texas with 14.
The CDC said more than 90 percent of patients with AFM since 2014 have been children younger than four years old.
Most of the kids with confirmed cases experienced a viral illness about a week before the onset of paralysis.
It's unclear if there is a greater risk of AFM in states that have a higher number of cases or if those states are just better at identifying and reporting patients.