OSLO, Norway (AP) _ A chemicals factory in southeastern Norway was the likely source of an outbreak of Legionnaire's Disease that has killed 10 people and infected more than 50, experts said Wednesday.

Tests showed the Legionella bacteria that caused the outbreak came from an air filtering system at the Borregaard plant in the southeastern city of Sarpsborg.

``We are almost completely certain that we have found the source of the outbreak,'' Svein Roensen, a local doctor, was quoted as saying by Norwegian media.

The first cases of the disease, particularly dangerous for older patients, were reported on May 21 in Fredrikstad, near Sarpsborg.

The ailment is caused by the Legionella bacteria, often carried by air conditioning and in water-cooling towers. The bacterium is not transmitted between people, and usually causes pneumonia or other lung ailments.

Legionnaire' disease can be treated with antibiotics, especially when caught in early stages. Death rates vary from 5 percent to 30 percent, with the elderly especially vulnerable. All of the dead in the latest outbreak were over the age of 70.

The disease takes its name from an outbreak in 1976 that killed 29 people at the Pennsylvania American Legion convention at a hotel in Philadelphia.