Netherlands reported a second case of dangerous Middle East Respiratory Virus, in a relative of the first person infected who had traveled to Saudi Arabia.
"The woman is a family member of the man who was diagnosed yesterday," the National Institute for Public Health and the Environment (RIVM) said in a statement on Thursday.
She was infected on the same trip to Saudi Arabia, where she spent two weeks sharing a hotel room with the man who was diagnosed on Wednesday, and visited a dromedary farm, the RIVM said.
The virus first emerged in Saudi Arabia in 2012 and recent research has suggested it may originate in camels.
The infected woman is in a stable condition and being treated in isolation at a hospital in the central Dutch city of Zwolle.
"Both patients have an underlying condition that apparently makes them vulnerable to infection from this virus," the RIVM said, without providing further details.
MERS causes fever, cough and shortness of breath, and can be lethal particularly among older people and those with pre-existing health problems.
Some 30 percent of the several hundred people infected with it have died, according to the US Centers for Disease Control and Prevention.
The vast majority of cases have been in Saudi Arabia, but MERS has also been found in 16 other countries. Most cases involved people who had recently traveled to Saudi Arabia.