Sen. Barbara Boxer is asking the Centers for Disease Control and Prevention for a formal investigation into what has caused polio-like paralysis in about 20 children in California over the past 18 months.

Boxer wants the agency to look into whether a virus is the culprit or if environmental factors are involved.

She also wants to know if the agency has any way of knowing if there are other unusual reports of paralysis nationally.

Learn more about the mystery illness.

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