There is no evidence that the strain is spreading in California or the U.S., and the risk of contracting Clade I mpox in the U.S. remains low.

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.

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.