Acute Flaccid Myelitis or A.F.M., predominantly happens in children and it's typically seen from August to October.
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The first outbreak started in late summer 2014, then another in 2016, and then the largest outbreak was 2018.
Since surveillance first started in 2014, there have been 570 confirmed cases in the United States.
AFM causes sudden and severe weakness to the limbs that can be permanent. It usually follows a viral illness. That's why researchers believe it's linked to viruses including enteroviruses, but it's still unknown why it happens to some children, and not others.
Even though there's a pattern of seeing a spike every two years, CDC experts say that could change.
They are urging healthcare providers to be ready to recognize and report cases right away to health departments. Parents should seek medical attention if their child develops weak limbs.
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