It's my supposition that, somehow, radiation reached the raw sewage that was dumped off the Long Island coast, and that within the radioactive sewage, the common plague bacillus mutated into a fast-growing and very virulent super-plague.

In the second-season episode "The Host" of The X-Files, the episode's main antagonist, a mutant creature dubbed "Fluke-Man" is traced to a Russian freighter that was carrying radioactive sewage away from Chernobyl.

Scully concludes her investigation, thinking that the creature was brought to the U.S. by a Russian freighter that was hauling salvage from Chernobyl, and that the creature was created in a 'soup' of radioactive sewage.