A mysterious polio-like illness that is sickening and in some cases paralyzing children is on the rise with at least 116 confirmed cases of acute flaccid myelitis so far this year, federal health officials said.

The latest number of confirmed AFM cases, spread across 31 states, is slightly more than double the number reported in October by the Centers for Disease Control and Prevention, which released its latest findings on Monday.

An additional 170 possible cases remain unconfirmed and under investigation, the CDC said.

AFM is an extremely rare but serious neurological condition that causes the body’s muscles and reflexes to become weak. Its cause remains unknown, and it generally affects children ― the average age of 4 ― more than adults. There is no vaccine or treatment, though health officials urge people to seek medical care immediately should they develop its symptoms, which typically begin with a mild respiratory illness or fever consistent with a viral infection.

The CDC last week established an AFM task force to help determine a cause and treatment for the condition, which is generally more prominent in the fall during the respiratory and flu season.

CDC’s #AFM Task Force will ensure that the full capacity of the scientific community is engaged and working together to provide important answers and solutions to detect, more effectively treat, and ultimately prevent AFM and its consequences. https://t.co/5u8FM2Hg8o — Dr. Robert R. Redfield (@CDCDirector) November 20, 2018

“I want to reaffirm to parents, patients, and our Nation CDC’s commitment to this serious medical condition,” CDC Director Robert R. Redfield said in a news release. “This Task Force will ensure that the full capacity of the scientific community is engaged and working together to provide important answers and solutions to actively detect, more effectively treat, and ultimately prevent AFM and its consequences.”

Colorado, with 15 confirmed cases this year, has had more cases than any other state. Texas has the second-highest number with 14.

CDC There are 116 confirmed cases of acute flaccid myelitis in 31 states, the CDC said.

The number of cases reported this year are not the highest ever seen.

In 2016 there were 149 confirmed cases in 39 states and D.C., while in the last five months of 2014 there were 120 confirmed cases in 34 states.

The number of AFM cases appears to rise every other year. Last year there were just 33 confirmed cases in 16 states, while 2015 saw just 22 confirmed cases in 17 states.