San Mateo County health officials have announced the nation’s first known case of a severe form of mpox that has fueled an outbreak of the disease across Eastern and Central Africa.

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.

The county of San Mateo has now had the first reported case of clade I mpox in the United States, according to the California Department of Public Health (CPDH). What is mpox? Mpox is an infectious disease that can cause a painful rash,