US confirms first case of more aggressive mpox strain

U.S. health officials confirmed on Saturday the first case of a more severe strain of mpox that infected an individual who recently traveled to Africa.

California health authorities identified the first known case of clade I mpox in the U.S. through laboratory testing. The person was treated in San Mateo County, according to the California Department of Public Health (CDPH). The individual is at home and recovering.

“People who had close contact with this individual are being contacted by public health workers, but there is no concern or evidence that mpox clade I is currently spreading between individuals in California or the United States,” California’s health department said.

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

“Historically, clade I has caused more severe illness than clade II, however, recent infections from clade I mpox may not be as clinically severe as in previous outbreaks, especially when cases have access to quality medical care,” CDPH wrote on Saturday.

Mpox is a disease that is caused by infection with a virus. In Africa, people have gotten it from small animal bites. Some of its symptoms include body aches, chills and fever.

On Nov. 22, the World Health Organization (WHO) will convene to determine if the outbreak of mpox in Africa still constitutes a public health emergency of international concern.

The new strain of mpox is different from the other, clade II, that caused an outbreak in 2022 in nonendemic nations. The WHO declared the recent outbreak of mpox in Africa a global health emergency in August.

The U.S. became the sixth nation outside of Africa to confirm the strain, according to the Centers for Disease Control and Prevention (CDC). Travel-related cases have been detected in India, Germany, Sweden, Thailand and the United Kingdom.

“The risk of clade I mpox to the general public in the U.S. remains low,” CDC wrote.