An 18-month-old boy has died of measles amid an outbreak in Berlin, a hospital in the German capital said Tuesday.

An autopsy on the child, who wasn't inoculated against measles, showed that he had an unspecified other disease as well but that wouldn't have led to his death without the measles infection, the Charite hospital said.

It is the first known death in an outbreak in which Berlin has recorded more than 570 cases since October.

Officials believe the outbreak began with a child asylum-seeker from Bosnia. They said it spread to the wider population partly because immunization rates among over-45s are low, and younger adults also are at risk because many only received one shot instead of two, as is now recommended.

Although it's rare for measles to be fatal in developed countries, the measles virus kills up to 10 percent of children infected in developing countries that have high levels of malnutrition and poor health care. Most measles deaths are caused by complications associated with the disease and are most common in children under five.

Measles is highly contagious and health officials say more than 90 percent of a population needs to be vaccinated to prevent outbreaks. Vaccination rates across Europe fell after a now-discredited study that suggested a link between autism and the vaccine for measles, mumps and rubella.

Health Minister Hermann Groehe called Monday for increased efforts to ensure that children are vaccinated and even suggested if that doesn't succeed, authorities might consider making it mandatory, though he said that isn't currently on the agenda.

A Berlin secondary school was closed as a precaution Monday because a student had measles, but reopened Tuesday. Officials checked students' and teachers' vaccination records and local health official Sibyll Klotz said five students who couldn't show that they were properly vaccinated were sent home, news agency dpa reported.

The German measles outbreak coincides with smaller ones in the United States tied to Disneyland in California and an Illinois day care center, which in total make up less than 150 cases. Officials say at least two of the measles cases in Berlin have been linked to the U.S. -- one person who developed symptoms there before traveling to Germany, and another who developed the infection after returning from the U.S.