MOORPARK, California—Lucian Olivera doesn't use canes because they slow him down. "They're wobbly," he says. Instead he prefers his walker or his leg braces—neither of which seem to slow down the rambunctious three-year-old. Though he can't walk, Lucian still bolts around the house, throwing and chasing his blue bouncy ball, unaware of the unusual circumstances that led to his disability.

Born more than 30 years after the last naturally occurring polio case was seen in the United States, Lucian was inflicted with a rare polio-like illness when he was 11 months old, leaving both of his legs paralyzed. He is not alone.

At least 20 confirmed cases of polio-like illness have been reported in the past two years scattered throughout California, leaving