Should an infected person be excluded from school or work?

Depends. On the infection and the importance of their work and their role there. If the infection is virulent and aggressive and they have a job where they see many people, certainly. If they have an infection that is not particularly virulent (e.g. Hiv) or a job where they can not be missed but don't expose many others, probably not. Use reason (hard to do).
R U contagious? That is the factor that determines whether or not you should be around others.
Contagious? An infected person should not be excluded. An infectious person should be. This is a decision best made by the individual's physician.