Andrew Noymer, an associate public health professor at the University of California, Irvine who has emerged as a leading voice on government response to the virus, suggests that may be the wrong track. On paper, a Bluetooth-based app that notifies a user they’ve been near someone who tested positive could help stem an outbreak, Noymer said. But he’s skeptical. It’s unclear how sensitive or accurate the tracking would be and how people without access to smartphones would be able to benefit from it. “I do think the privacy, the encroachment, concerns are nothing to be dismissed out of hand,” he added.