While that's a possibilty, you have to understand that bubonic plague is endemic in parts of the rodent population of the western US. Earlier in the 20th century, bubonic plague did spread into the US. While it didn't create a massive pandemic among humans, it did manage to get a foothold among the rodents. Just as there's a endemic foothold for the disease in Mongolia (the source of previous great plagues such as the Black Death), there's been one in the US for decades. Of course, living conditions in the US are light years from medieval Europe and Asia in the 1300's, so the disease doesn't turn into an epidemic.
There's actually a non-kook community of scientists who do not believe Bubonic Plague was the cause of the Black Death.
There is also a very large rat population this year...because of the rains.