A polio-like illness that paralyzes children is on the rise in the U.S. again two years after an outbreak caused alarm to doctors and parents.

The U.S. Centers for Disease Control and Prevention reported on Monday, Oct. 3, that for this year alone, 50 cases of acute flaccid myelitis have already been reported in 24 states across the U.S.

The illness remains rare but the number of cases has more than doubled compared with last year. In 2015, only 21 cases of AFM were confirmed for the whole year.

The agency has been actively investigating the illness starting August 2014, when an increasing number of people across the U.S. reported to have AFM for which the cause was not determined.

"We continue to receive reports of sporadic cases of AFM," the CDC said. "From January 1 to August 31, 2016, a total of 50 people in 24 states across the country were confirmed to have AFM."

Most patients struck by AFM experience sudden weakness in at least one arm or leg as well as loss of muscle tone and reflexes. In addition to limb weakness, some patients also experience difficulty moving the eyes, facial droops, drooping eyelids, difficulty with swallowing or slurred speech.

The condition typically starts with a fever or respiratory illness before the neurological symptoms start to show up and prevent the movement of the limbs.

Nearly all of those affected show inflammation of the gray matter in the spinal cord. Of the children affected, 85 percent showed improvements albeit very few fully recovered.

AFM has been linked to a strain of enterovirus. Enteroviruses often cause mild illnesses such as colds, but they can cause serious problems when they infect the central nervous system.

Mosquito-borne viruses such as the West Nile virus is also known to cause AFM, so health experts recommend using mosquito repellent when going outdoors and staying indoors at dusk and dawn when mosquitoes tend to bite.

The CDC likewise recommended being up to date on all vaccinations including vaccines for poliovirus to protect the family from a disease that can cause AFM.

The CDC said that observing good hygiene can help stop the illness from spreading. It recommended frequent washing of the hands with soap and water, avoiding close contact with people who are sick and using disinfectant to clean surfaces that a sick person has touched.

"Washing your hands the right way is one of the best things you and your children can do to protect against getting sick," the CDC said.