The number of children being stricken by a mysterious paralyzing condition continues to increase, federal officials say.
At least 252 cases of acute flaccid myelitis, or AFM, have been reported to the Centers for Disease Control and Prevention so far this year from 27 states, including 90 that have been confirmed through Nov. 9, the CDC reported Tuesday.
Most of the cases have occurred among children between the ages of 2 and 8.
The illness usually starts as a fever and seemingly routine respiratory symptoms. But in some cases — between three and 10 days later — children suddenly suffer paralysis.
The cause of the condition remains a mystery. But officials say there is a possibility it is being caused by a virus that affects the digestive system known as an enterovirus, though that remains just a theory.
Another possibility is that the condition is being caused by an overreaction of the immune system to an infection. Also under investigation are rhinoviruses, which cause the common cold and other respiratory illnesses.
Regardless, public health officials say they are racing to try to determine the cause and the best treatments.
"As a mom, I know what its like to be scared for your child. And I know parents want answers," Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said during a briefing for reporters. "We've learned a lot about AFM since 2014, but there are things we still don't understand."
No one has died from the condition so far this year, she noted, adding the condition remains rare.
In about half of cases, the patients eventually fully recover. But the other half appear to be left with permanent disabilities, Messonnier says.
AFM outbreaks appear to occur every two years, with most cases occurring in the late summer and fall. The pace of cases this year appears to be on track to have the same number as in the past few outbreaks, Messonnier says.
While environmental toxins remain a possibility, Messonnier says that seems unlikely given how widespread the cases are.
She also encouraged parents to continue to get their children vaccinated, saying vaccines don't appear to be a possible cause. There is no evidence the condition is being caused by the polio virus.
"We are trying to figure out what the triggers are that would cause AFM," Messonnier says.
AILSA CHANG, HOST:
Health officials are trying to figure out why a growing number of children are developing a rare, paralyzing condition. NPR health correspondent Rob Stein has an update on the investigation by the Centers for Disease Control and Prevention.
ROB STEIN, BYLINE: The condition is known as acute flaccid myelitis, or AFM, and Nancy Messonnier at the CDC says it usually starts with the kind of thing lots of kids get this time of year.
NANCY MESSONNIER: Most patients with AFM have fever and/or respiratory symptoms before developing AFM. However, at this time of year, many children have fever and respiratory symptoms.
STEIN: And most end up just fine. But something scary suddenly happens to some children. Otherwise healthy, active kids suddenly start to go limp. Their arms and legs get paralyzed three to 10 days later. That's AFM.
MESSONNIER: In almost all patients, an upper limb was involved. About half had only upper limb involvement.
STEIN: The CDC says the number of reports of these cases has now climbed to 252 so far this year, including 90 that have been officially confirmed as AFM. Most of the cases are kids between the ages of 2 and 8. About half the kids eventually fully recover, but the other half are left with some kind of long-term, sometimes serious disability.
MESSONNIER: As a mom, I know what it's like to be scared for your child. And I understand parents want answers.
STEIN: So scientists are racing to try to figure out what's causing this. Tests have found some common viruses in some of the patients, but it's too soon to know if any of them are causing AFM or it's something else.
MESSONNIER: It may be one of the viruses that we've already tested. It may be a virus that we haven't yet detected. Or it could be that the virus is kicking off another process. Those are all hypotheses that we're looking closely at. Right now, the science doesn't give us an answer.
STEIN: In the meantime, Messonier urges parents not to panic. AFM is very rare. It doesn't appear to be related to any kind of toxin in the environment or vaccines. So it's important that parents get kids flu shots and other vaccines that will protect them from much more common, serious health problems. Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.