First Locally Spread Cases of Severe Mpox Strain Detected in the U.S. 🇺🇸

LOS ANGELES, California —

U.S. health officials have confirmed the first locally spread cases of a more severe strain of mpox, marking a significant development in the country’s public health landscape.

According to the Los Angeles County Department of Public Health, three residents tested positive for the Clade I variant of mpox this week — the first such cases confirmed to have spread within the United States rather than through international travel.

Previously, the mpox infections reported in the U.S. were linked to a different clade of the virus, which tends to cause milder symptoms. However, the newly identified Clade I strain has been associated with more severe illness, raising concerns among health experts.

“These cases show that the more virulent form of mpox can spread domestically,” said local health officials in an Oct. 17 statement. “We are closely monitoring for additional infections and advising caution.”

So far, there have been nine confirmed Clade I mpox cases nationwide in 2025, most of which were tied to travel abroad. The three new California cases represent the first known community transmission of this strain in the U.S.

Public health authorities are urging healthcare providers to remain alert for symptoms — including fever, rash, and swollen lymph nodes — and to report suspected cases immediately to prevent wider spread.