From January through July of this year, 32 people have been diagnosed with a strange polio-like illness called Acute Flaccid Myelitis (AFM) — a condition that causes a sudden onset of weakness in one or more arms or legs, according to the Centers for Disease Control and Prevention. The disease, which may hit record highs in 2016, is not well understand, though scientists are trying to determine how long the paralysis lasts, as well as its cause and how to best treat it.

“CDC is looking at these trends very carefully,” CDC official Manisha Patel told The Washington Post. “We have sent out several health alerts to states to let them know we are seeing an increase in reporting and to encourage them to communicate with doctors to report these cases in a timely fashion.”

Through July 2016, 17 states have confirmed cases of AFM, but Patel declined to reveal which specific states. Of the 32 cases this year, only three of the children have fully recovered. During a 2014 outbreak of AFM, the CDC verified reports of 120 children in 34 states who developed the disease between August and December of that year. AFM occurs mostly in children and only occasionally affects adults.

“We are definitely hearing of cases from our colleagues across the country,” Teri Schreiner, a neurologist at the University of Colorado and Children's Hospital Colorado, told The Post. “It’s a trend that’s worrisome … what I'm hearing from others seems to be coming at a tempo similar to what happened in 2014.”

In 2015, there were 21 cases of AFM across 16 states. The numbers have risen steadily since April of this year.

Currently, the CDC is looking to identify a cause of AFM in the United States and working with healthcare professionals and state and local health departments to investigate and better understand the illness.

Read more:

Mystery Illness Acute Flaccid Myelitis Spreads To Kids Across US: Is It Caused By The Enterovirus?

A Polio-Like Illness Is Paralyzing Children, And We Don't Know What's Causing It