"The hunt for the source of infection is over. We have, to a high degree of likelihood, found the source," Svein Rønsen said at the press conference.

Industrial concern Borregard in Sarpsborg has been named as the probable source of the Legionella bacteria.

A purifying installation known as a scrubber, which cleans air using water, is considered the precise source.

"Such facilities spread large amounts of water vapor through the air," communicable disease authorities said at the press conference.

The result came as a surprise to investigating authorities as such facilities have never caused a Legionnaires' outbreak before, either in Norway or abroad.