Synopsis

A rare and virulent bacteria is claiming victims throughout the city, prompting Chicago's first responders to collaborate with the CDC in an effort to contain the escalating crisis. A fire at a nearby university, linked to the outbreak, has Severide questioning the scope of the problem. The story continues in *Chicago Med*, Season 5, Episode 4, "Infection, Part II," and *Chicago P.D.*, Season 7, Episode 4, "Infection, Part III."