The number of children being stricken by a mysterious paralyzing condition continues to increase, federal officials say.

At least 252 cases of acute flaccid myelitis, or AFM, have been reported to the Centers for Disease Control and Prevention so far this year from 27 states, including 90 that have been confirmed through Nov. 9, the CDC reported Tuesday.

Most of the cases have occurred among children between the ages of 2 and 8.

The illness usually starts as a fever and seemingly routine respiratory symptoms. But in some cases between three and 10 days later children suddenly suffer paralysis.

The cause of the condition remains a mystery. But officials say there is a possibility it is being caused by a virus that affects the digestive system known as an enterovirus, though that remains just a theory.

Another possibility is that the condition is being caused by an overreaction of the immune system to an infection. Also under investigation are rhinoviruses, which cause the common cold and other respiratory illnesses
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