Erin Olivera waited weeks for doctors to tell her why her youngest son was paralyzed.
Ten-month-old Lucian had started crawling oddly — his left leg dragging behind his right — and soon was unable to lift his head, following Erin only with his eyes.
She took him to a hospital in Los Angeles, but doctors there didn't know how to treat what they saw.
Lucian's legs felt soft as jelly and he couldn't move them. His breathing became rapid. The left side of his smile drooped as his muscles weakened.
Physicians ran test after test, and Erin began spending her nights on a hospital room couch. After Lucian fell asleep, during her only minutes alone between working and visiting her three other kids, she cried.
A terrifying reality was taking hold: Doctors wouldn't be able to give her a diagnosis for her paralyzed child.
"How can I make a decision for him when I don't even know what's wrong?" she said. "What can I do to help him?"
So one morning in July of 2012, Erin lifted Lucian out of his hospital bed, his body limp and heavy. She rested his cheek on her shoulder, the way he liked to be held since he'd become weak.
Erin returned home to Ventura County with a child she thought might never learn to walk.
In the years since, hundreds of children across the country have shown up at hospitals unable to move their arms or legs. Dozens of kids have become paralyzed in the past few months alone.
They suffer from a mysterious illness that continues to alarm and puzzle scientists. This kind of sudden and devastating paralysis hasn't been widespread since the days of polio. Lucian, one of the disease's earliest victims, set off a hunt among doctors to discover its cause.