Health officials have been trying to trace where COVID-19 came from and where it’s going. In some countries, including China, South Korea, Singapore and Israel, they’ve used cellphones and apps to identify and monitor people infected with the virus. Now, Silicon Valley giants Apple and Google are trying to create the technology for the U.S. But they need more of your data. Guest: Rachael Myrow, senior editor of KQED's Silicon Valley desk