"Today I tested positive for COVID-19. I'm resting and taking it easy for a few days. Grateful to be vaccinated and boosted!" she tweeted.
Kotek won the Democratic primary election in May. She previously served as speaker of the Oregon House of Representatives.
Prior to her announcement, Kotek tweeted photos from over the Fourth of July holiday weekend that show her at a Portland Pickles game and hiking in Silver Falls State Park.
Oregon lifted its indoor mask mandate in mid-March due to dropping COVID-19 cases and hospitalizations. Cases and hospitalizations began to rise again in late April and continued to climb throughout June.
Peter Graven, lead forecaster for Oregon Health and Science University, said he expects COVID to keep spreading through July.
He said omicron subvariants BA.4 and BA.5, both of which have come on strong in Oregon after initially remaining in the background during prior weeks when BA.2 and BA.2.12.1, were driving most of the state's cases.
Health officials said the two slightly newer subvariants are now responsible for more than half of new cases in the state.
The increased spread has prompted the Centers for Disease Control to raise the COVID-19 transmission risk level to high in most Oregon counties, including Oregon’s most populated places.