WASHINGTON (AP) -- Democratic Sen. Barbara Boxer has asked the federal Centers for Disease Control and Prevention to initiate a formal investigation into what has caused polio-like paralysis in about 20 children in California over the past 18 months.
Boxer's letter, sent Thursday to CDC Director Thomas Frieden, says "we need answers."
In particular, she wants the agency to examine whether the illness can be traced to a virus or environmental factors. She also wants to know whether the agency is aware of similar reports of paralysis nationwide.
In a statement emailed to The Associated Press, the CDC said Frieden received the letter "and will be giving it careful consideration."
Doctors at Stanford University said earlier this week that they had found some instances of children suffering paralysis in one or more limbs.