Rare. This is a childhood/infant infection that used to be a feared epidemic disease lethal to many. Recent nonesense about vaccinations has led to pockets of recurrence in areas where the local climate drops the number vaccinated below the numbers needed for "herd" protection. Most docs will never see a case but a doc in an area with low rates may see a bunch.
Yes. In my area and practice, we had an outbreak in 2012 with 100's of cases. We saw about 40 cases last year (2012) in our office. So not so rare..