Early last spring, as flu season hit its peak, a woman checked into a Houston hospital with all the familiar symptoms: fever, headache, a grating cough. A chest x-ray revealed an infection engulfing her lungs. Doctors hooked her up to an antibiotic drip, collected blood to be processed and cultured in the hospital’s lab, and shipped one of the tubes overnight to a small, stealthy startup in Redwood City, California, called Karius.