Rush, 75, said in a pair of tweets that he's fully vaccinated and hasn't had any symptoms.
"Today, after being notified of a recent exposure, I tested positive with a breakthrough case of COVID-19. Fortunately, I am fully vaccinated and recently received my booster shot. I am feeling fine," he said.
Rush said he's following guidance from the Centers for Disease Control and Prevention and will be quarantining.
Rush is one of almost a dozen lawmakers to announce that they've tested positive since Dec. 18, when Rep. Matt Cartwright, D-Pa., said he'd tested positive and was experiencing mild, flu-like symptoms. Rush's announcement brings the number of House members who say they've tested positive to eight; three senators have also tested positive.
All of the lawmakers have said they are vaccinated and have been experiencing mild or no symptoms. The spike in Congress has come as there has been a surge in cases in Washington, D.C., and other areas of the country thanks to the omicron variant of the coronavirus that has killed over 800,000 people nationwide.
Hospitalizations around the country have risen 39 percent from Nov. 1 to last week, according to an NBC News analysis of data from the Department of Health and Human Services.
The Washington Post reported Tuesday that data show that healthy vaccinated people, especially those who've gotten booster shots, appear unlikely to develop severe infections from the omicron variant.