Federal health officials are worried about an increase in a mysterious and rare condition that mostly affects children and can paralyze arms and legs, with 127 confirmed or suspected cases reported as of Tuesday.

Of those, 62 cases of acute flaccid myelitis, or AFM, have been confirmed in 22 states, said Nancy Messonnier, a top official at the Centers for Disease Control and Prevention. More than 90% of the confirmed cases have been in children 18 and younger, with the average age being 4.

The surge in cases has baffled health officials, who on Tuesday took the unusual step of announcing a change in the way the agency will count cases. They also wanted to raise awareness about the frightening condition so parents can seek medical care if their child develops symptoms, and so reports of the illness can be quickly relayed back to the CDC.

“We understand that people, particularly parents, are concerned about AFM,” said Messonnier, director of the National Center for Immunization and Respiratory Diseases. Despite extensive laboratory and other testing, CDC has not been able to find the cause for the majority of the cases. “There is a lot we don’t know about AFM, and I am frustrated that despite all of our efforts, we haven’t been able to identify the cause of this mystery illness.”


Increases in AFM cases have occurred in 2014 and 2016, usually in August and September, Messonnier said at a news briefing with reporters. The CDC knows of one child who died with the disorder in 2017.

Since officials have been unable so far to determine how the disease spreads, they are starting to count suspected cases as well as confirmed ones to better anticipate increases in confirmed cases over the coming months, she said.

There is no specific treatment for the disorder, and long-term outcomes are unknown. The rare but serious disorder affects a person’s nervous system, specifically the spinal cord. Neurological conditions like it have a variety of causes, such as viruses, environmental toxins and genetic disorders.

Among the cases under investigation are five reported to Maryland health officials in recent weeks, a health department spokeswoman said Tuesday. Maryland’s first case was reported Sept. 21. No known cases have been reported in Virginia or the District of Columbia this year, but there were three confirmed cases in Virginia in 2016, health department officials said.


“We know this can be frightening for parents, and I know many parents want to know what signs and symptoms they should be looking out for in their children,” Messonnier said. Parents should seek medical care right away if their child develops sudden weakness or loss of muscle tone in the arms and legs.

Some patients diagnosed with this condition have recovered quickly, but some continue to have paralysis and require ongoing care, she said.

CDC began tracking the condition in 2014, when there were 120 confirmed cases. Then in 2016, there were 149 confirmed cases. Officials said it’s too early to know whether the total for 2018 will surpass those previous years. But the data reported Tuesday represents “a substantially larger number than in previous months this year,” Messonnier said.

She said it was important for parents and clinicians to remember that this is a rare condition, affecting less than 1 in 1 million people under age 18. “As a parent myself, I understand what it’s like to be scared for your child,” she said. “Parents need to know that AFM is rare even with the increase in cases we are seeing now.”


Still, because this is a “pretty dramatic disease,” Messonnier said health officials want to raise awareness about the symptoms to make sure parents seek medical care immediately if their children show a sudden onset of weakness in their arms and legs.

The agency knows that poliovirus is not the cause of these cases because CDC has tested every single stool specimen from patients, and none have tested positive for poliovirus. Messonnier said West Nile virus, which had been listed as a possible cause on CDC’s website, is not causing the illnesses.

In some individuals, health officials have determined that the condition was from infection with a type of virus that causes severe respiratory illness.

So far, the CDC has found no relationship between vaccines and children diagnosed with AFM from the 2014 cases. Officials will be conducting additional analysis on this year’s cases.


“Our medical team has been reviewing vaccine records when available during this year’s investigation and do not see a correlation,” CDC spokeswoman Kristen Nordlund said. The disorder has been diagnosed in children who have received some of their recommended vaccinations and in unvaccinated children, she said.

The agency doesn’t know who may be at higher risk for developing this condition or the reasons they may be at higher risk. CDC has tested many specimens from patients with this condition for a wide variety of pathogens, or germs, that can cause AFM. But so far, no pathogen has been consistently detected in the patients’ spinal fluid.

Parents can best protect their children from serious diseases by taking prevention steps, such as washing their hands, staying up to date on recommended vaccines and using insect repellent to prevent mosquito bites, Messonnier said.

There is no specific treatment for AFM, but neurologists who specialize in treating brain and spinal cord illnesses may recommend certain interventions, such as physical or occupational therapy, on a case-by-case basis.


Benjamin Greenberg, a neurologist who has treated children with AFM at the University of Texas Southwestern in Dallas, said AFM is “exquisitely rare.” But, if their child is diagnosed, parents should prepare for extensive physical therapy — therapy that isn’t always covered by insurance, he said. Some children paralyzed by AFM have eventually regained their ability to walk but need time.

“Families really sticking with it are seeing slow but steady recovery,” he said.

CDC is not releasing a list of the 22 states with confirmed and suspected cases because of privacy issues. But some state health departments have been making public their reported cases. States are not required to provide this information to CDC, but they have been voluntarily reporting their data.