First US locally transmitted mpox clade I cases in California

Three cases of a more severe form of mpox have been confirmed in California, health officials said, marking the first known instances in the United States of local transmission of the clade I strain. One case was identified in Long Beach and two in Los Angeles. All three patients had no recent travel to regions where clade I is endemic, were hospitalized early in their illness and have since been discharged to recover at home in isolation while investigators work to determine how they were infected.

Public health departments in Long Beach and Los Angeles said the cases represent an unusual development because clade I has largely been confined to central and eastern Africa and had not previously been shown to spread locally in the United States. Officials described clade I as generally causing more severe illness than the clade II strain that drove the 2022 outbreak in the United States. Symptoms can begin with fever, fatigue and other flu like signs and often progress to a painful rash and lesions. Health officials noted antiviral treatments may be considered for people at risk of severe disease.

Los Angeles County has reported a rise in mpox infections this year, with more than...