The only thing I can figure (pulls theory out of ass) is it must have had something to do with those areas being so interconnected economically to the maritime industries and the navy. Ships were coming and going all the time, and since tyhpus is spread by infested fleas and lice on rats, in an area where you would have a seaport it's not unlikely you could have outbreaks. Like the way the bubonic plague got it's initial toehold in seaport towns.

But that's just a guess.