It had been a rough few months. Cynthia Tompkins was hospitalized in May for osteomyelitis — a bone infection — then spent six weeks in a rehabilitation facility. “It was a struggle,” she said. “I didn’t bounce back too well.” Tompkins returned to her home in San Diego, but she was still taking antibiotics, along with a host of other drugs for diabetes, pain, and blood clots. The deaths of her husband the previous year and her closest friend more recently had sapped her spirits. In early July, a new symptom appeared: violent vomiting three times within about 24 hours. “I was so depleted,...