A Viral Disease

Mpox is a viral disease that spreads through close (skin to skin), intimate and sexual contact with an infected person. Mpox can cause a painful and itchy rash on hands, feet, chest, face, or mouth or near the genitals. Other symptoms include fever, chills, swollen lymph nodes, exhaustion, muscle aches and backache, headache, sore throat, nasal congestion, and cough.

Current Situation

San Mateo County Health is responding to case of clade I mpox.

Clade I & Clade II

According to the Centers for Disease Control and Prevention, there are two types of mpox, clade I (with subclades Ia and Ib) and clade II (with subclades IIa and IIb; IIb caused the ongoing global outbreak). A clade is a genetic branch of the disease.

The risk of exposure for the public to clade I mpox remains low, but there continue to be sporadic clade II mpox cases in the United States. Casual contact, such as during travel, in an office or classroom or in a store, is unlikely to pose significant risks for transmission of either clade of mpox.

Mpox Outbreaks

Outbreaks from the different subclades can have different characteristics, like 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 only recently been reported in the United States. 

Travel-associated cases have also been reported in Germany, India, Kenya, Sweden, Thailand, and Zimbabwe. Historically, clade I mpox has caused more severe illness and deaths than clade II mpox; however, recent data demonstrate that infections from clade I mpox in the current outbreak may not be as clinically severe as in previous outbreaks.

What to Do

Travelers to countries experiencing clade I outbreaks should consult with their primary health care provider.

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.

For More Information

More information about mpox is available from the California Department of Public Health and the Centers for Disease Control and Prevention.