The Centers for Disease Control and Prevention has been unable to get to the bottom of the sudden spike in a rare illness that paralyzes children.

"I am frustrated that despite all of our efforts we have not been able to find the cause of this mystery illness," Dr. Nancy Messonnier, director at the CDC's National Center for Immunization and Respiratory Diseases, said in a call with reporters Tuesday.

Officials describe the illness, known as acute flaccid myelitis, or AFM, as similar to polio. It affects the nervous system by weakening patients' muscles, making moving difficult and causing a facial droop as well as slurred speech.

Health officials suspect as many as 127 people are infected across 22 states, where they are under investigation. Sixty-two are confirmed to have AFM.

[Read: Amy Klobuchar urges CDC to investigate spread of polio-like illness]

The agency has urged parents and their children to immediately seek medical care if they suddenly develop weakness in their arms or legs.

Scientists aren't precisely sure what causes AFM, but they think it may result from a viral infection. Neurological issues such as these are often triggered by viruses, genetic conditions, or something in the environment.

So far the CDC has been able to knock out other causes that have been culprits in the past – including the respiratory illness enterovirus; the cold-causing rhinovirus; and West Nile Virus, which is carried by mosquitoes.

CDC has opened the door to investigating other causes, such as toxic chemicals in the environment.

"This is a mystery so far and we haven't found it yet, so we have to be thinking broadly," Messonnier said.

While the majority of people who become infected are under the age of 18, about 10 percent of those who have been infected are adults. The average age of infection is four years old.

While officials have stressed that the illness remains rare, it is still very serious, and Messonnier referred to it as a "dramatic disease."

Children who become infected are sometimes hooked up to a ventilator in the intensive care unit to help them breathe. Some children recover while others can become paralyzed. Last year one child died after becoming ill.

"We don't know who is at higher risk or the reasons why they may be at higher risk," Messonnier said. "We don't fully understand the long-term consequences."

At least 386 patients have been infected with the illness since 2014, and it has no cure. The latest outbreak surpasses last year's total but is still short of the 149 cases reported in 2016.

The CDC has issued guidance saying people need to be up to date on vaccines, wash their hands, and prevent mosquito bites. Officials announced during the call on Tuesday that they would be posting updates to the number of infections on its website every Monday.