(CNN) There have been 80 confirmed cases of the polio-like illness known as AFM in 25 states this year as of Friday, the US Centers for Disease Control and Prevention said Monday.

In addition, there are 139 cases under investigation for a total of 219 confirmed and suspected.

This is eight more confirmed cases than the agency reported last week and 20 additional patients under investigation.

The CDC noted an increase in reports of patients under investigation who began experiencing symptoms in August, September and October. It has not identified the 25 states with confirmed illnesses, nor has it said how many states are reporting cases under investigation.

AFM, or acute flaccid myelitis, is a rare illness that affects the nervous system, especially the gray matter in the spinal cord, and can cause muscle weakness and sudden onset of paralysis. Last month, the CDC said that 90% of patients since 2014 have been children under the age of 4, although adults can also develop AFM.

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