Down with the Sickness

You hurl a slimy mote of infectious gunk at a creature within range. Make a ranged spell attack against the target. On a hit, the target must make a Fortitude saving throw. On a failed save, the target is knocked prone and begins showing symptoms of magical illness: sneezing, shivering, and coughing. While infected, the creature takes 1d6 "Cold" damage at the start of each of its turns for 4 rounds.

The damage increases by 1d4 for every 4 caster levels (e.g., 2d4 at 4th level, 3d4 at 8th, etc.).