The United States has beaten many illnesses, including the plague. But many of the diseases once thought defeated are making a comeback and it is likely due to the massive amounts of unscreened illegal immigrants who are entering the country many of whom are carriers for diseases like the plague.

Another contributor can be cities with high rat and homeless populations like New York, Chicago, Portland, and Los Angeles. All of the uncleanliness in those cities can contribute to the plague spreading too.