A 25-year-old living in Reno, Nevada, appears to be the first U.S. case of someone getting the 2019 novel coronavirus twice, according to an early, not-yet-peer-reviewed study from researchers in the state.

Scientists at the University of Nevada, Reno School of Medicine and the Nevada State Public Health Laboratory describe someone who had a mild case of COVID-19—the disease caused by the virus—in April. They said he got it again in May, with more severe symptoms that required hospitalization and oxygen.

The news comes after Hong Kong researchers said they identified someone being infected for a second time there, and two European cases appeared to represent reinfections in Belgium and the Netherlands.