The first known case of clade I mpox in the U.S. was recently discovered in a person in California, the Centers for Disease Control and Prevention said Saturday.

The individual had just traveled from Eastern Africa where there is an ongoing outbreak, the CDC said. They were treated shortly after returning to the U.S. at a local medical facility and released, according to the California Department of Public Health.

The person has since isolated at home, is not on treatment specific for mpox and symptoms are improving, according to the health agency.

The California Department of Public Health confirmed the case through lab testing after determining a plan of action based on the person’s travel history and symptoms. Specimens are being sent to CDC for additional viral characterization and, the CDC said, it is working with the state to identify and follow up with potential contacts.

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According to the CDC, 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.)

There’s no way to tell which type of mpox someone has by looking at them. Outbreaks from the different subclades of mpox can have different characteristics, like who they affect, how they’re spread or how many deaths they cause, according to the CDC.

Although clade II mpox has been circulating in the U.S. since 2022, clade I mpox has never been reported in the U.S. before now, the CDC said. But the health agency said the risk to the public remains low.

People with mpox often get a rash that may be located on hands, feet, chest, face, mouth and/or near the genitals. The CDC said the incubation period is 3–17 days, and, during this time, a person does not have symptoms and may feel fine.

The CDC said you can protect yourself from mpox by:

• Avoiding close contact with people who are sick with symptoms of mpox, including those with skin or genital lesions
• Avoiding contact with contaminated materials used by people who are sick (such as clothing, bedding, toothbrushes, sex toys, or materials used in healthcare settings)
• And if you’re eligible, get both recommended doses of mpox vaccine

The CDC said it continues to work in Central and Eastern Africa to help stop mpox transmission at the source including laboratory training, supplies for diagnostic testing, training of frontline health and epidemiologic workers and other mitigation strategies.