The Robert Koch Institute, a government scientific and health research organization, reported the findings on Wednesday, as concern over the virus grows ahead of the 2016 Summer Olympics in Brazil.

"We're working under the assumption that those infected came down with the virus while traveling," said a spokeswoman for the institute in an interview with newspaper "Neue Osnabrücker Zeitung."

Since October, 56 cases of people infected with Zika have been reported in Germany. A month ago, the government announced it was requiring those who were infected to register.

Zika cases possibly underreported

In her interview with the newspaper, however, the spokeswoman acknowledged that the number of Zika cases in Germany might in fact be higher.

"It wouldn't be surprising if the cases were underreported, since the symptoms for the disease are mild and infected people often don't see a doctor," she said.

The virus, which is transmitted by ordinary mosquitoes, has spread rapidly through the Americas starting in early 2016, prompting fears over the impact it will have on the Summer Olympics in Rio de Janeiro. However, the World Health Organization (WHO) said last week that it would not be necessary to postpone the summer games, since the virus has already been reported in some 60 countries.

On Tuesday, the WHO issued a public statement advising tourists coming from Zika-infected areas not to have unprotected sex for at least eight weeks after the end of their trip.

blc/msh (dpa, epd)