The case marked the first known instance of that particular mpox variant appearing in the United States. A different variant of the virus, called clade II, has been circulating in the U.S. since 2022 and has sickened at least 108 people in the county, the agency said.

The first case in the U.S. of a more severe strain of mpox was reported in San Mateo County, the California Department of Public Health said.

San Mateo County health officials said on Saturday they have reported the first known case of clade I mpox in California and the United States. According to the San Mateo County Health, a person became infected with the clade I mpox after traveling in ...