Confirmed cases of acute flaccid myelitis, a rare condition characterized by rapid onset of flaccid weakness in one or more limbs and spinal cord gray matter lesions, have climbed to 90 in 27 states this year, the CDC reported Tuesday.
At least 252 cases have been under investigation so far this year, including a burst of 33 cases in the past week, according to Nancy Messonnier, MD, director of the National Center for Immunization and Respiratory Diseases at the CDC.
Most confirmed acute flaccid myelitis cases involved children, ages 2 to 8 years, and "almost all reported fever or respiratory illness in the 3 to 10 days before limb weakness," Messonnier said in a press briefing.
The CDC said that no deaths have been reported this year, but on Tuesday, parents of children with acute flaccid myelitis say that two boys died of the disease. While unable to comment directly on the claims, a CDC official told CNN there could be a "lag" in terms of when it receives each report.
The condition remains a mystery: no pathogen has been found consistently, though nearly all patients have reported signs and symptoms consistent with viral illness in the weeks preceding limb weakness.
"It may be one of the viruses that we have already detected," Messonnier said. "It may be a virus that we haven't yet detected. Or it could be that the virus is kicking off another process and it's actually triggering, through an autoimmune process, acute flaccid myelitis. Those are all hypotheses that we're looking closely at."
Acute flaccid myelitis appears to peak every other year. It of enterovirus (EV)-D68, but when the number of acute flaccid myelitis cases rose again in 2016, the CDC did not have reports of large outbreaks of severe respiratory illness, noted Susannah McKay, PhD, of the CDC, and co-authors in an early-release .
The CDC conducts enterovirus and rhinovirus testing on patients who meet the clinical criteria for acute flaccid myelitis when specimens are available, they added. So far, 125 clinical specimens from 71 patients -- including 21 cerebrospinal fluid (CSF), 59 upper respiratory, and 45 stool or rectal swab specimens -- have been tested in 2018. Specimens from 38 patients (54%) were positive by real-time reverse transcription-polymerase chain reaction testing: 11 for EV-A71, 14 for EV-D68, and 13 for other viruses, primarily from non-sterile sites.
While the number of confirmed cases is three times what it was at the same point in 2017, "it would certainly be premature to project how many cases we're going to see this season," Messonnier said. "So far, the curve from 2018 looks similar to 2016 and to 2014."
"It's important for parents to realize that this still is a relatively rare condition," she added. "We've been working really hard this year to make sure that clinicians know about it so that they can detect it and report it to the health department."
The CDC offers , including information about acute flaccid myelitis and instructions to help clinicians report patients under investigation to local and state health departments.