San Mateo County health officials said on Saturday they have reported the first known case of clade I mpox in California and the United States.
According to the San Mateo County Health, a person became infected with the clade I mpox after traveling in Eastern Africa, that's where there is a current outbreak of the strain. Another strain of mpox, called the clade II, has been circulating in the U.S. since 2022.
San Mateo County health officials added the person has mild symptoms and is currently recovering at home. The county is also contact tracing anyone who might have been in contact with the infected person.
Officials said that the threat of clade I mpox to the public remains low at this time.
"The risk to the general population is low," said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. “After exposure, in about 4-7 days, you get flu-like symptoms, so headache, muscle aches, fever. But 2-3 days after that, you start getting these boils that people know about from 2022.”
The United States is the sixth country outside Africa to have detected the clade I strain, according to the CDC, which can cause more severe illness than the version of the virus that spread widely in 2022.
The spread of this strain through several African countries prompted the World Health Organization to declare a global public health emergency in August, the second time mpox has been introduced in two years.
Chin-Hong said it's unclear how the new strain might spread in the U.S. However, some experts anticipate it could spread among the same sexual networks as Clade II did in 2022.
“The one that we saw in 2022 is mainly confined to men who have sex with men," he said. "[I]f you got one shot, make sure you get the second.”
