A San Mateo County resident was diagnosed with the first known case in the United States of a certain variation of mpox, known as clade I mpox, the county's health department and California Department of Public Health said on Saturday.
The CDPH and San Mateo County Health said in dual press releases that the person was isolating at home with mild illness and recovering. It said health officials did not believe clade I mpox was spreading in the community and close contacts were being notified with help from the U.S. Centers for Disease Control and Prevention.
The person is believed to have acquired clade I mpox based on their travel history to East Africa, according to San Mateo County Health and the CDC. There is currently an outbreak of the viral disease in Central and East Africa that was declared an emergency by the World Health Organization in 2022.
The genetic strain is different than clade II mpox, which the county has already had cases of since the global outbreak two years ago. While 108 cases of clade II mpox have been diagnosed in San Mateo County, this is the first case of clade I mpox. Clade I mpox can cause more severe illness and deaths, according to the CDC and county health department.
But the CDC also said the most recent outbreak of clade I mpox has been less severe than previous outbreaks. While previous global death rates from clade I mpox have been between 3-11 percent, the more recent outbreak has death rates of about one percent, which could be less in countries with strong healthcare systems.
Transmission of mpox, formerly called monkeypox, comes through close, intimate skin-to-skin contact, according to the CDPH. It is unlikely to spread through casual contact, such as classroom, work or travel settings. It presents as a rash.
