An outbreak of a mysterious illness with symptoms similar to polio has reached Georgia. This year, three children across the state have been diagnosed with acute flaccid myelitis (AFM), an illness that causes respiratory issues, muscle weakness and varying degrees of paralysis.

Since the CDC started investigating the condition in 2014, the agency have seen nearly 400 confirmed cases of AFM around the U.S., almost entirely in children. Seventy two of those cases are from 2018, spanning across 24 states. Over the past few years, the majority of cases have occurred between August and October.

The CDC is currently investigating the cause of the illness, but results have been relatively inconclusive. Although AFM looks similar to polio symptomatically, patients have been tested for poliovirus, and the CDC confirmed that patients with AFM do not have a variation of polio. However, scientists are investigating whether or not there is a link between AFM and enteroviruses, rhinoviruses, or West Nile virus.

The condition is extremely rare, but the recent uptick in cases since 2014 prompted the ongoing CDC investigation. The CDC reports that although viral infection seems to be the most likely cause of AFM, they noted that it could possibly be caused by environmental toxins.