(CNN) - With 24 newly confirmed cases of the polio-like illness acute flaccid myelitis announced Monday, 2018 has become a record year for the illness.
In its weekly update on cases of the illness, the US Centers for Disease Control and Prevention said there have been 158 confirmed cases in 36 states this year.
This is the highest number of confirmed cases in a single year since the CDC began tracking cases in August 2014. Since then, there have been a total of 484 confirmed cases of AFM, according to the CDC.
The illness has peaked every other year in the fall.
From August to December 2014, there were 120 confirmed cases. In all of 2015, 22 confirmed cases were reported. In 2016, there were 149 confirmed cases, and in 2017, 35 confirmed cases were reported.
In addition to the confirmed cases reported this year, there are 153 patients under investigation as possibly having AFM.
Last week, the CDC said the number of cases this year seemed to have peaked, as indicated by a decline in the number of patients under investigation. The decline was expected to continue, with fluctuation in the number of confirmed cases; some of those under investigation would be confirmed while others would be eliminated.
This week's report holds true to expectations. The number of patients under investigation is 12 fewer than last week, while the number of confirmed cases jumped.
Although it's not clear what exactly causes AFM, the CDC said, "Most of the patients with AFM (more than 90%) had a mild respiratory illness or fever consistent with a viral infection before they developed AFM."
More than 90% of AFM patients have been children.
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