Esperanza rising. After the dust storm, Mama is the only one of the workers in the cabin to become ill, why is this so?

The doctor said that Valley Fever often affects people who have recently moved to the area and aren't used to the air.

"It's a disease of the lungs caused by dust spores. Sometimes, when people move to this area and aren't used to the aire here, the dust spores get into their lungs and cause an infection."