What is already known about this topic?
A clade I monkeypox virus (MPXV) outbreak is ongoing in the Democratic Republic of the Congo. Travel-associated clade I MPXV infections have been reported in non-African countries.
What is added by this report?
The first reported clade Ib MPXV infection in the Americas was identified via electronic laboratory reporting in California in a U.S. traveler who returned from East Africa. Rapid identification allowed for thorough contact tracing; no secondary cases were identified.
What are the implications for public health practice?
Public health authorities should be notified immediately of suspected clade I MPXV infections (e.g., compatible symptoms and travel history, or compatible laboratory results [e.g., presence of nonvariola orthopoxvirus with no detection of clade II MPXV]) to trigger additional testing and enable rapid implementation of transmission-based precautions and other public health interventions.