And for now, it's hard to say if 2018 will equal or surpass spikes seen in 2014 and 2016, Messonnier said, adding that state and federal health officials haven't finished the whole diagnostic algorithm for numerous cases reported over the past several weeks.
Health officials in 22 states have reported at least 62 confirmed cases of acute flaccid myelitis in 2018 so far, according to the Centers for Disease Control and Prevention. Messonnier added that health officials are considering other potential causes, such as West Nile virus and environmental toxins, though none of the cases have involved them.
Since the condition was first recognized by CDC in 2014, the agency has confirmed 362 cases.
"We actually don't know what's causing this increase", said Dr. Nancy Messonnier, of the CDC. CDC experts say the overall rate of AFM is about one in a one million.
"We have not been able to find a cause for the majority of these AFM cases", she said.
AFM is a condition in which the gray matter of the spinal cord becomes damaged, leading to muscle weakness and paralysis in one or multiple limbs.
Additional symptoms can include facial drooping or weakness, difficulty swallowing and slurred speech.
"What parents have to know is if your child suddenly has a weak arm or leg, is not speaking properly, has a stiff neck or a wobbly neck - call the doctor immediately", pediatrician Dr. Laura Popper said. Officials have been baffled by the increase, and are starting to count suspected cases as well as confirmed ones to better anticipate increases in confirmed cases over the coming months.
The agency knows that poliovirus is not the cause of these cases because the CDC has tested every single stool specimen from patients and none have tested positive for poliovirus.
Some patients diagnosed with this condition have recovered quickly, but some continue to have paralysis and require ongoing care, she said. One child died from AFM in 2017.
Messonnier stressed that while she understands how frightening this situation is for parents, they should remember that the infections are, in fact, rare. "We recommend seeking medical care right away if you or your child develops sudden weakness of the arms and legs", she said.
In research developments, a team based at the J. Craig Venter Institute conducted experiments to see if a specific EV-D68 genotype is linked to neurologic symptoms and found that some viruses from the 2014 outbreak can infect neuronal cells.
Officials have not determined a cause of the rare disease.
The CDC is actively investigating and monitoring disease activity and recommends taking standard prevention measures such as hand-washing, protecting oneself from mosquito bites and staying up-to-date on vaccinations. States are not required to provide this information to CDC, but they have been voluntarily reporting their data.
The CDC referred calls to individual state health departments.