Redwood City, CA – The work of San Mateo County Health’s disease investigation and public health laboratory teams was featured in the February 13, 2025, issue of the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report (MMWR). The scientific journal is the main communications platform for federal disease investigators and local epidemiologists and other professionals, in the public and private sectors, to share timely and noteworthy public health information.

In November 2024, County Health responded to the first case known case in the United States of clade I mpox. Outbreaks of mpox from the different subclades, or genetic branches, can have different characteristics, including whom they affect, severity and how they’re spread. Although clade II mpox has been circulating in the United States since 2022, clade I mpox had not been reported in the United States until the local case. Confirmed through laboratory testing, the case was related to an ongoing outbreak of clade I mpox in Central and Eastern Africa and was acquired through travel.

County Health’s communicable disease investigators first identified the case through its surveillance of reports and information from local health care providers. Given the national importance of this case and the need for an outbreak response that involved multiple states and countries, County Health coordinated with the Centers for Disease Control (CDC) and the California Department of Public Health. County Health investigators monitored the patient, traced contacts for potential exposure and swabbed and tested specimens to prevent transmission and contain the infection. With the rapid identification of the case and these containment efforts, no secondary cases or further spread of mpox was detected.

After its lead role in the response, San Mateo County Health was asked by the CDC to serve as first authors of the scholarly paper to appear in the MMWR about the outbreak.

Lead authors were Staff Physician Vivian Levy, MD, Communicable Disease Investigator Anna Branzuela and Public Health Laboratory Director Kristina Hsieh, DrPH. Also acknowledged for their work were Health Officer Kismet Baldwin-Santana, MD, and Communicable Disease Investigators Munya Mahiya and Wesley Yuen.

Subsequent unrelated travel cases of clade I mpox appeared in Georgia in January and New Hampshire and New York in February 2025. Even before the publication of the MMWR through the CDC, local health authorities and clinicians received health messaging related to this investigation. The publication further spreads awareness and best practices to health care professionals for identifying and containing a potential outbreak of clade I mpox.

“I was proudest when a respected CDC colleague who had managed multiple national and international outbreaks said in a call, ‘This is how it is supposed to work,’” said Levy.

The MMWR is available online at the CDC’s website.

Preston Merchant

Communications Officer

San Mateo County Health 650-867-1661

press@smchealth.org