LOS ANGELES, June 26 -- The man in Long Beach had not traveled internationally. He had not returned from a country where mpox clade I was circulating, had no known contact with anyone who had. When the rash appeared, painful pustular lesions that he initially mistook for something routine, it was several days before a clinician ordered the specific laboratory assay that identified what he had. By the time results came back, he was one of three unrelated Southern California residents whose combined diagnoses told California's public health officials something they had been watching for since late 2024: the more severe form of mpox had crossed from returning traveler to local community and was spreading without a passport.

On June 16, the ...