San Mateo County Health is monitoring symptoms in individuals who may have been exposed to clade I mpox, following the confirmation of the first known case of this strain in the United States on Saturday, Nov. 16.
The health department’s sexually transmitted infection team received the positive test result late last week and has since launched a comprehensive contact investigation, according to County Health Officer Kismet Baldwin-Santana.
The infected individual has been directed to follow the Centers for Disease Control and Prevention and California Department of Public Health guidelines, which require isolation until lesions have scabbed over, new skin has formed, and full recovery is achieved.
“We have spoken to any facilities that this person may have visited, and we are also reaching out to any staff who may have been exposed,” Baldwin-Santana said.
The case is linked to an ongoing outbreak of clade I mpox in Central and Eastern Africa and is believed to have been acquired through travel.
The county declined to disclose the patient’s city of residence or provide additional details.
A county press release stated on Saturday there is no concern or evidence of clade I mpox spreading among individuals. Transmission typically spreads from skin to skin, intimate and sexual contact.
Baldwin-Santana added that historically, clade I has been associated with more severe symptoms compared to clade II, which already has 108 cases in the county. The Jynneos vaccine, which was widely administered during the 2022 mpox outbreaks, is effective for both clade I and clade II.
She advised those concerned about potential exposure to consult their primary care providers and follow recommendations outlined by the CDC and CDPH.
