You go out to get groceries or to see your doctor or just a walk around the block. You may or may not have the virus. Someone you encounter may or may not have the virus. But later on you or one of those people you passed find out that they have the virus. How do you backtrack to to figure out who in your travels may have been infected?
What's needed is a smartphone app that, as you're moving around, connects to each and every OTHER smartphone carried by the people you encounter, and tags that smartphone with connection information. If any one of that set of people later find that they have the virus, the app would be used to directly contact them and advise them of the potential exposure.
As it stands now infected people are simply asked, "Who did you encounter over the past 14 days?", and who can possibly know that? But it's critical in tracking the spread and treating infected people as soon as possible, even before the symptoms show up.
I don't know enough about inter-phone communications to even know where to begin developing an app like that. But someone must.