The CDC says it's looking into at least 80 confirmed cases of a polio-like illness, and is investigating over 200 more.
Officials say the number of patients who began experiencing symptoms of acute flaccid myelitis, or AFM, in August, September and October was higher than in any other month this year.
AFM is a neurological condition that targets the spinal cord. It can cause weakness in the limbs, paralysis and even death. It usually affects children but can potentially be prevented by regular vaccinations, hand-washing and mosquito-bite protection.
CDC data from the last four years shows that in 2018, confirmed cases of the condition are almost triple what they were last year. But they're still below confirmed cases in 2014 and 2016.
The CDC says it's actively investigating the cases, but as of now, the cause of most of them is still unknown.