BERLIN – Authorities in Berlin say a spike in measles infections has been traced to unvaccinated refugees but at least two measles cases appear to have come from the United States.

Berlin has recorded 468 cases of measles this year, more than the rest of Germany had during all of 2014.

Dr. Dirk Werber of Berlin’s state health office said Friday that a child asylum seeker from Bosnia is considered the index case because many subsequent infections among refugees were genetically identical.

Measles has since spread to Berlin’s non-refugee population, partly because immunization rates among over-45s are low.

Werber said one woman and possibly a child appeared to have contracted measles while travelling in the United States.

Some 100 people have been sickened by a recent measles outbreak in North America.