Is my boss required to inform me if one of our coworkers has coronavirus?

This is more of a legal question. They have a duty of care to you. They also have a duty of care to those that are sick to not share medical information. Management are almost certainly under no obligation to share private medical data of their employees.

You say people got sick at the sister store. So it sounds like there is no risk to people at your own store? If people are moving between stores, that is a different story.

Unfortunately no and unfortunately I don't think you'd have a solid lawsuit against them. You might have a class action suite against them but they will win. In most cases they'd just settle to avoid costly lawyer and court fees though.

There are several incidences over the years where companies knowingly used or allowed their employees to use unsafe practices. Take for example the glow in the dark watches. Companies knew for a long time that the stuff was toxic and extremely damaging to bodies yet they used these group of women that regularly licks the paintbrushes so they can apply it to a small watch handle.

Coronavirus is really no different from anything else a company might know about. A company does not need to disclose it to their employees as they can argue people would already know it is dangerous and contagious. And they can even argue that you do not have to come to work and you are free to go elsewhere if you feel unsafe. Generally this will hold up in courts unless they somehow put a sick person into work.

Heck, recently talcum powder was linked to cancer and the company knew about it for decades but continued to supply it to their customers. The worst thing that happened is they set aside a high interest account with a set amount of money to just give people as lawsuits come in. Once the money is gone, chances are no one can sue them ever again about it and they get away free and clear despite having killed numerous people.

The grocery store I work at (in canada mind you) has said they will inform us if a confirmed case is in the store (customer or staff). I'm not sure if this is a legal requirement but I think it is just a decision our store has made to tell staff and customers if there has been a case in the store. They obviously can't disclose personal information but personally I would want managment to tell us if the virus was found to be in the store.