A device for administering a fluid includes a sterilization cassette having a shell, a fluid chamber, and an ultraviolet light transmitting window. An input tube directs fluid into the chamber. An ultraviolet light source is positioned to direct ultraviolet light through the window into the fluid chamber at an intensity sufficient to kill or render non-reproducible at least one species of a microorganism in the fluid while the fluid is in the chamber. An outlet tube receives fluid from the cassette and directs the fluid to a destination. The fluid is substantially uniformly exposed to the light while in the chamber. The cassette and light source are contained in a housing that prevents ultraviolet light from escaping the housing.