First case of severe mpox disease reported in major city: ‘Life-threatening’ | 16 March 2026 | The first case of severe mpox (formerly monkeypox) has been identified in New York City, according to an advisory issued by the NYC Health Department. One resident has tested positive for mpox clade I, one of the two main genetic groups (clades) of the mpox virus, which causes the illness. “Clade I causes more severe symptoms and can be life-threatening,” Dr. Marc Siegel, Fox News senior medical analyst, told Fox News Digital. The New York City patient recently traveled out of the country, the advisory states. “This appears to have come here from travel and has not spread locally,” Siegel noted. [Do not comply.]