A Nevada man became the first published case of Covid-19 reinfection in the U.S., adding to a growing number of examples world-wide signaling that patients who have recovered from the viral disease might still be at risk of getting it again.

In a paper in the medical journal Lancet Infectious Diseases, a group of authors including University of Nevada researchers recount the case of a 25-year-old who suffered two bouts of Covid-19 infection, one confirmed through testing in mid-April and the second in early June. Symptoms of the second case started in late May, a month after the patient reported his initial symptoms as having resolved.

The two strains of virus were genetically distinct, signaling that it is unlikely that the man simply remained unknowingly infected with the virus in one, longer bout, the authors wrote. The paper notes that the patient’s second case of Covid-19 was more severe than his first, requiring supplemental oxygen and admission to a hospital after he suffered from shortness of breath.