The California Department of Public Health confirmed, through laboratory testing, the first known case of clade I mpox in the United States. This case is related to an ongoing outbreak of clade I mpox in Central and Eastern Africa.
The risk of clade I mpox to the public remains low, and there continue to be sporadic clade II mpox cases in the United States.
The case was diagnosed in a person who recently traveled from Eastern Africa. The individual was treated shortly after returning to the United States at a local medical facility and released. Since then, the person has isolated at home, is not on treatment specific for mpox, and symptoms are improving. Based on their travel history and symptoms, patient specimens were tested and confirmed for the presence of clade I monkeypox virus. Specimens are being sent to CDC for additional viral characterization. Additionally, CDC is working with the state to identify and follow up with potential contacts.
Casual contact, like you might have during travel, is unlikely to pose significant risks for transmission of mpox.
The anticipated overall risk of clade I mpox to the general population in the United States from the outbreak in Central and Eastern Africa is low. Earlier this year CDC conducted a risk assessment which included epidemiologic data from Central and Eastern Africa, data from the ongoing mpox outbreak in the United States caused by clade IIb, and historical data on clade I mpox outbreaks in DRC and other affected countries. In addition, CDC has simulated clade I mpox outbreaks. These simulations indicate that close-contact transmissions within and between households are unlikely to result in a large number of mpox clade I cases in the United States. Additionally, in Sweden, Thailand, Germany, and India there was no apparent onward spread of the virus and the onward spread in the United Kingdom has been limited to close, household contacts so far.
CDC continues to work in Central and Eastern Africa to help stop mpox transmission at the source. This ongoing work includes laboratory training, supplies for diagnostic testing (including genetic sequencing), training of frontline health and epidemiologic workers, support for surveillance in people and animals, support for infection prevention and control, risk communication and community engagement, and direct technical assistance in outbreaks, as well as research collaborations.
