MEMPHIS, Tenn. — The Shelby County Health Department on Monday reported 31 confirmed cases of the omicron variant of COVID-19, which has now become the dominant strain nationwide.

Dr. Michelle Taylor with the health department reported the area’s seven-day rolling average at 267 new cases per day. That’s up from 94 just three weeks ago.

The new seven-day rolling average is the highest number since the delta variant surge on Oct. 27, which was 275 cases per day.

Omicron accounted for 73% of new infections last week, federal health officials said Monday.

The Centers for Disease Control and Prevention numbers showed nearly a six-fold increase in omicron’s share of infections in only one week.