An unauthorized cheese factory in the northern Portuguese town of Baiao, 370 km north of Lisbon, is the source of an outbreak of brucellosis in the area, which has so far led to 13 confirmed infections, according to local press reports on Tuesday.

Brucellosis, which is also known as Malta Fever, Rock Fever or Mediterranean Fever, is most often contracted from unpasteurized milk or milk products such as cheese. The disease leads to parasites in the host’s bloodstream and episodes may last weeks, months or even years. It causes potentially recurrent episodes of high fever, sweating and related anemia.

At least four of the victims of the outbreak have been hospitalized in the neighboring city of Porto, a spokesperson from the Northern Regional Health Administration told the Expresso newspaper.