In an unusual pattern that adds to the mystery of acute flaccid myelitis (AFM), the paralytic syndrome in children is peaking every other year in a fall seasonal pattern that began in 2014.
For example, after few cases were reported last year, the Centers for Disease Control and Prevention received increased reports of suspect cases in August, September, and October in 2018.
“There have been reported cases of AFM in many countries, but nobody else has detected this very particular pattern of disease with this seasonal clustering every other year,” Nancy Messonnier, MD, director of the CDC National Center for Immunization and Respiratory Diseases, said at a recent press conference.
A pattern of emergence and retreat would seem to suggest a particular pathogen or cause, but the CDC has not been able to determine a unifying diagnosis that would explain the majority of cases. The CDC has continued to test isolates and track AFM cases since the syndrome dramatically increased in 2014.
“The number of cases reported in this time period in 2018 is similar to what was reported in the fall of 2014 and 2016,” she said.
In contrast, AFM cases have been widely dispersed over many states since it emerged. “We are looking for clues, but we really haven’t seen it in the geography,” Messonnier said.
The following timeline for AFM cases is summarized below from CDC reports.1,2
2014: From August to December, 120 people in 34 states were confirmed to have AFM. This coincided with a record outbreak of enteroviruses (EV)-D68 that resulted in some 1,200 confirmed cases in 49 states. Although the EV-D68 is a known cause of AFM, it was not detected in sufficient numbers of the AFM patients to be considered the sole cause of the emergence.
2015: Cases drop, with a total of 22 people in 17 states confirmed to have AFM.
2016: Cases rose with a total of 149 people in 39 states and Washington, DC, confirmed with AFM.
2017: Cases fall, as the CDC confirms only 33 cases of AFM in 16 states.
2018: The seasonal pattern holds, with cases rising again. As of Nov. 2, 2018, the CDC reported 80 confirmed cases of AFM in 25 states across the U.S. In addition, another 139 unconfirmed cases are under investigation.