Scientists at the Centers for Disease Control and Prevention (CDC) are collaborating with the Massachusetts Department of Public Health to investigate a situation in which a U.S. resident tested positive for monkeypox on May 18 after returning to the U.S. from Canada.

CDC is also tracking multiple clusters of monkeypox that have been reported in early- to mid-May in several countries that don’t normally report monkeypox, including in Europe and North America.

It’s not clear how people in those clusters were exposed to monkeypox but cases include people who self-identify as men who have sex with men. CDC is urging healthcare providers in the U.S. to be alert for patients who have rash illnesses consistent with monkeypox, regardless of whether they have travel or specific risk factors for monkeypox and regardless of gender or sexual orientation.