It's usually 1 of 2 reasons. Lack of reporting or increase in active cases. When Omicron arrived a few weeks ago, our active case number jumped from a steady 50-60 to over 1400. Not a big number for a US city, but in a place with 7 ventilators it's significant.

Numbers are coming back down; below 1000 again and declining everyday. Unfortunately, the CDC is very slow to update their ratings so expect a level 4 for at least a month.