This is Part 1 of OneChicago's 2019/20 crossover, continuing with Infection, Part II (2019) (Chicago Med, S05E04), and finishing with Infection, Part III (2019) (Chicago P.D., S07E04).
Engine 17 and Truck 46 are mentioned on scene of the fire at the lab. Both are fictional units also used in the movie Backdraft.