First U.S. case of clade I-type mpox found in California.

The California Department of Public Health identified the first case of the clade I type of mpox in the United States, the Center for Disease Control and Prevention said on Saturday. While the U.S. has had an ongoing outbreak of clade II mpox since 2022, clade I can be more medically serious, resulting in serious illness or death. While clade II has been transmitted mostly by same-sex sexual contact, clade I is transmitted by additional means—by contact with infected animals, infected members of the same household, and even contaminated objects, according to the John Hopkins Center for Health Security.

The groundbreaking case in California is linked to an ongoing clade I outbreak across East and Central Africa, where the patient recently traveled. The public risk mpox remained low with the patient isolated at home, health officials said. The disease was first called monkeypox because it was observed in research monkeys.

What does mpox look like? People contracting mpox usually develop a fever and other flu symptoms like swollen lymph nodes, chills, and muscle aches, according to the Cleveland Clinic. Mpox may also cause a rash on one’s hands, feet, chest, mouth, and genitals.

Wasn’t clade II mpox already in California? Mpox clade II has circulated in the state since 2022, according to the California Department of Public Health. The CDC identified Clade I as a more aggressive mutation, causing more severe illness, and deaths. State officials insisted that the public risk of contracting mpox remained low.

Dig deeper: Read Josh Schumacher’s report about a clade I mpox variant case in Europe earlier this year.