According to the CDC, an outbreak is "a chain of transmission including 3 or more cases linked in time and space." So, that does mean that throughout the country we've had a number of small, isolated outbreaks. But none of them have been found to be connected to one another. If 107 people across 21 states were all sick from a single outbreak, that might be far more concerning because it would suggest there could be much more spread. Some outbreaks happen in pockets of unvaccinated people who would all be at risk, for instance, while others spread via travel. The famous Disney World outbreak in 2015 was so troublesome for that reason. If people get infected in one place, then travel and spread measles to many other states, you're broadening the pool of people who could potentially get infected. Most measles outbreaks are actually quite small. From 2009 through 2014, the median outbreak size was just 5 cases.