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.
The odds of getting the polio-like disease is less than one in a million; however, two cases in the Bay State have been confirmed and four others are under investigation, the Department of Public Health announced.
The CDC said the condition isn't new, "but the increase in cases we saw starting in 2014 is new".
The average age of children is about 4, she said, and 90 percent of cases the CDC has been studying since 2014 have involved children 18 or younger.
"This is a mystery so far", the CDC's Dr. Nancy Messonnier said in a call Tuesday with reporters.
The CDC also does not yet know who may be at a higher risk for developing AFM or the long-term consequences of the condition.
CDC officials say they haven't found the cause.
In addition to viruses, potential causes may include environmental toxins and genetic disorders, according to the CDC, and it "can be hard to diagnose because it shares numerous same symptoms as other neurologic diseases". Despite extensive laboratory and other testing, CDC has not been able to find the cause for the majority of the cases.
European Union calls for new proposals from Theresa May to break Brexit deadlock
Yesterday, Mrs May appealed for her Cabinet to "stand together and stand firm" at a marathon two-and-a-half hour meeting in Downing Street.
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. Other symptoms may include trouble moving the eyes, drooping eyelids or facial droop and weakness. The first case in Maryland this year was contracted September 21, a spokeswoman for the department said in an email. "As a parent myself, I understand what it's like to be scared for your child", she said.
There have been no confirmed cases of AFM in Maine this year, according to Emily Spencer, spokesperson for the Maine Department of Health and Human Services and the Maine CDC.
"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", she said.
"This is actually a pretty dramatic disease", she said.
More broadly, she noted, "there is a lot we don't know about AFM". The disease is being called acute flaccid myelitis, or AFM, and although researchers suspect that it's caused by a virus, no virus has yet been discovered that's associated with the condition.
The CDC knows of one death in a child who had AFM in 2017, Messonnier said. In 2016, there were 149 cases.
There is no specific treatment for AFM, but doctors may recommend physical or occupational therapy to help with arm or leg weakness.
States are not required to provide this information to the CDC but have been voluntarily reporting their data.