US health officials confirmed the country’s first case of a more severe strain of mpox on Saturday, involving an individual who had recently traveled to Africa.

California health authorities identified the case as clade I mpox through laboratory testing. The patient, treated in San Mateo County, is currently recovering at home, according to the California Department of Public Health (CDPH).

“Public health officials are reaching out to individuals who had close contact with the patient, but there is no indication that clade I mpox is spreading within California or the U.S.,” stated California’s health department.

The outbreak of clade I mpox originated in Central and Eastern Africa.

“Historically, clade I has been linked to more severe illness than clade II. However, recent infections may not be as severe, particularly when patients receive quality medical care,” CDPH noted.

Mpox is a viral disease that has been transmitted to humans in Africa, primarily through bites from small animals. Symptoms include fever, body aches, and chills.

On November 22, the World Health Organization (WHO) is set to review whether the mpox outbreak in Africa still qualifies as a public health emergency of international concern.

This newly detected strain differs from clade II, which was responsible for the 2022 outbreak in nonendemic regions. The WHO had previously declared the ongoing mpox outbreak in Africa a global health emergency.

The US has now become the sixth country outside of Africa to confirm a case of clade I mpox, following detections in India, Germany, Sweden, Thailand, and the United Kingdom, according to the Centers for Disease Control and Prevention (CDC).

Despite the confirmed case, the CDC emphasized that the overall risk of clade I mpox to the general public in the US remains low.