By Gary Evans, Medical Writer 

Acute flaccid myelitis (AFM) is continuing to increase in the U.S., causing paralytic symptoms of unknown origin in children.

All signs point to a virus of some type, but the Centers for Disease Control and Prevention cannot pinpoint an etiological agent that would provide a “unifying diagnosis” for all cases.

As of Nov. 13, 2018, the CDC was investigating 252 patients with AFM, with 90 cases confirmed in 27 states, Nancy Messonnier, MD, director of the CDC National Center for Immunizations and Respiratory Diseases, said at a recent press conference.

Enterovirus D68 (EV-D68) and EV-A71 have been known to cause AFM in the past, but neither virus is being singled out as the prime cause of the outbreak. The CDC has tested 125 spinal cord fluid respiratory and stool specimens from 71 of the confirmed cases.

“Of the respiratory and stool specimens tested, about half were positive for enterovirus or rhinovirus, including EV-A71 and EV-D68,” she said. “The spinal cord fluid was positive in two cases. One had evidence of EV-A71, and one had evidence of EV-D68. One of the cases was in an adult who was on immune-suppressive medication, and the other was in a child who had very rapid progression of paralysis.”

Putting these cases in context, Messonnier said the presence of a pathogen in respiratory secretions or stool is less definitive in making a diagnosis than finding it in the spinal column.

“When a pathogen is found in the spinal fluid, it is good evidence that it was the cause of a patient’s illness," she said. "However, oftentimes, despite extensive testing, no pathogens are found in the spinal fluid.”

One explanation could be that the pathogen has been “cleared by the body” and is hard to detect, Messonnier said. “Another possibility is that the pathogen triggers an immune response in the body that causes damage to the spinal cord.… We’re trying to figure out what the triggers are that would cause someone to develop AFM.”

With enteroviruses being detected in some respiratory and stool samples from patients with AFM, some press members asked the CDC why that was not being identified as the cause of the outbreak. One reason is that—unlike with previous AFM outbreaks—there has been no corresponding increase in enteroviruses at this time, Messonnier noted.

 “CDC is a science-driven agency,” she said. “Right now, the science doesn’t give us an answer.”