[user_50123890]

This reassures the hypothesis that you probably won't catch the virus from a brief contact in a grocery store or similar if you keep your distance.

Infections happen within families, and spread from one family to another by friends/coworkers. The infected people should be easily able to list all exposed out by name.

An exception is of course mass indoors public events that are forbidden now. This is where a contact tracing app would probably prove to be the most useful.

[Retric]

Incidental contact is unlikely to matter in most cases. However, multiple people at different tables where infected at a restaurant from a single customer. So, it doesn’t take that much.

[eloff]

Or on public transport. New York's subway system was probably it's Achilles heel during this outbreak.

[dehrmann]

Except Staten Island had the second most cases per capita. Lots of the obvious NYC theories have holes where you look at places affected.

[jmull]

People who live or work on Staten Island used mta services, including subways, heavily.

[adrianmonk]

Maybe ferries cause the same kinds of problems as subways do.

[cozzyd]

Yes Public transport is probably the best use case for contact tracing. A combination of location history and fare card data will work for buses. For trains it's a bit trickier since you want to resolve that you're in the same car, and Bluetooth would work well in this case.

[bhelkey]

I see these methods as a way to capture in depth contact between strangers (Public transportation, Lyft/Uber, ...) and to double check our memories.

[cma]

How about that restaurant study where lots of people at tables behind the guy next to the air conditioner flow got it:

https://www.nytimes.com/2020/04/20/health/airflow-coronaviru...