Workers disinfected a cooling tower at the Østfoldhallen shopping center on Sunday. As many as 30 other cooling towers in the region were also being inspected. PHOTO: JON HAUGE

Legionnaires' Disease

The so-called Legionnaires' bacteria thrives in water and dirt, and started spreading when air conditioning systems became more common in the 1950s. The disease was first identified in 1976, after hundreds of war veterans from the American Legion fell ill after attending a convention in Philadelphia. More than 30 died. Symptoms The disease has an incubation period of two to 10 days, while five to six days is most common. Those infected begin experiencing high fevers, a dry cough, muscle aches, fatigue, stomach pain and diarrhea. The disease can be treated with antibiotics.

A woman in her 70s became the fourth victim of the Legionnaires' outbreak. She died during the night, according to officials at Østfold Hospital. Seven others remain in intensive care, and more than 70 have been admitted to hospital with Legionnaires'-like symptoms.

Health authorities, meanwhile, remained unable on Monday to pinpoint the source of the disease. Cooling towers for air conditioning systems, where the bacteria is known to appear, were being checked and disinfected, especially in the Fredrikstad-Sarpsborg area.

That's where the first cases started being diagnosed late last week. Health officials in Fredrikstad, just north of the Swedish border, feared an epidemic like one that hit Stavanger four years ago.

Doctors and nurses at the central hospital serving the Fredrikstad-Sarpsborg region worked through the weekend to try to chart the movements of the four victims of the disease and the 24 who have been diagnosed with it. They admitted it was difficult work, because many of the patients were too sick to answer many questions.

Two patients died of the disease at Østfold Hospital on Sunday in addition to the death on Monday. It's also been determined that another person who died from a lung ailment on May 19 also was infected with the Legionnaires' bacteria. All four came from Sarpsborg and Fredrikstad.

Four persons were listed in criticial condition and on life support systems on Monday. A total of 71 persons were admitted to hospital over the weekend with pneumonia-like systems and others were being tested.

Hospitals in Oslo were standing by to take in patients if necessary, while a team of experts was helping out from Stavanger, where Legionnaires' Disease killed seven persons in 2001. That outbreak was later traced to a hotel's air conditioning system.