It would be useful if people who have tested positive for the virus could flag people and locations they came into contact with in the days before they became symptomatic.
This might be useful on a variety of levels:
1) informing the potentially exposed individuals without requiring the patient to individually contact each person
2) let others avoid those who have a higher probability of exposure (or at least give them a data point to help them make a risk-benefit estimate)
3) identify "hot spots" (businesses, restaurants, etc)
4) making the spread or potential spread of the virus more tangible for people who don't personally know anyone who has contracted the virus
Plus it would just be a fascinating dataset for visualizing the spread through communities.
Of course, I see the potential for this to exacerbate panic and enable social shaming/exclusion. I expect the perception that you're "throwing people under the bus publicly would decrease utilization of this tool even if it existed. Any ideas for how to avoid that perception?
Seems like this could be implemented pretty easily on top of Facebook APIs for Friends and Business Pages.