Redwood City – San Mateo County Health is working with state and federal partners in responding to a case of clade I mpox, the first known case in the United States. Confirmed through laboratory testing, the case is related to an ongoing outbreak of clade I mpox in Central and Eastern Africa and was acquired through travel. The risk of exposure for the public to clade I mpox remains very low, but there continue to be sporadic clade II mpox cases in the United States.
Since 2022, County Health has responded to the global outbreak of clade II mpox. Outbreaks from the different subclades, or genetic branches, can have different characteristics, including whom they affect and how they’re spread. Although clade II mpox has been circulating in the United States since 2022, clade I mpox has never been reported in the United States until now. Historically, clade I mpox has caused more severe illness and deaths than clade II mpox.
San Mateo County Health is assisting the California Department of Public Health and the Centers for Disease Control and Prevention on tracing and notifying close contacts of potential exposure.
To date, 108 cases of clade II mpox have been reported in San Mateo County.
“While clade I may be new to the United States, we and other counties have been responding to mpox since 2022 with contact tracing, guidance and vaccine support,” said San Mateo County Health Officer Dr. Kismet Baldwin-Santana. “Our work continues, with the support of our state and federal partners.”
With mild illness, the individual is isolating at home and recovering. There is no concern or evidence that mpox clade I is currently spreading among individuals in San Mateo County or elsewhere in the United States.
Transmission typically spreads from close (skin to skin), intimate and sexual contact. Casual contact, such as during travel, in an office or classroom or in a store, is unlikely to pose significant risks for transmission of mpox. Travelers to countries experiencing clade I outbreaks should consult with their primary care provider.
“Given the very low risk to the public of exposure to clade I,” said Dr. Baldwin-Santana, “the standing guidance for preventing mpox has not changed.”
Persons who have certain risk factors should consult with their primary health care provider about vaccination and take steps to reduce exposure, including avoiding close, skin to skin contact with people who have a rash that looks like mpox and avoid contact with objects and materials that a person with mpox has used.
More information about mpox is available from the California Department of Public Health and the Centers for Disease Control and Prevention.
Preston Merchant
County Health Communications Officer
650-867-1661
pmerchant@smcgov.org