Ford has announced that Donald Tafoya, a Cleveland Casting Plant employee who died a week ago, has tested positive for the Legionella (Legionnaire's disease) bacterium. It had previously been thought that Tafoya died of pneumonia.

Tafoya is the first Ford worker to die of the disease, which is caused by a bacteria often inhaled in contaminated vapour from air conditioners, steam or other sources.

On Tuesday, two Ford workers from the Cleveland plant were confirmed as having Legionnaire's and Ford closed the plant on Wednesday when a third employee was diagnosed with the disease.

"On behalf of Ford Motor Company, I extend my deepest sympathies to the family of our employee," said Roman Krygier, vice president, powertrain operations, at Ford.

"We want to reiterate that our company is taking extraordinary measures to deal with this issue. We are cooperating fully with all public health authorities."

Earlier, Ford and the Cuyahoga County Board of Health had said that investigations were continuing into the three cases of Legionnaires' disease confirmed among employees mid-week.

No source of the illnesses had been identified, the company and health authority said in a joint statement.

The Centres for Disease Control, the Ohio Department of Health, the Cuyahoga County Board of Health, Ford and the UAW are conducting the joint investigation.

It includes environmental sampling and assessments of conditions at more than 120 locations inside the plant and results from will be available in five to 10 days.

The agencies are concurrently conducting an epidemiological investigation and are monitoring pneumonia and pneumonia-like illnesses to determine if there are other cases of Legionella.

Ford has hired a national expert, Clayton Industries of Novi, Michigan, to help with the process of disinfecting potential sources in the plant, such as showers, heating and air-conditioning systems, and water used in the casting process.

Ford is finalising plans with the Board of Health for disinfection and will start as soon as the CDC completes its sampling. The disinfection process uses chemicals, such as chlorine, and heat for sterilisation.

The plant, employing 2,224 hourly and 276 salaried workers, is expected to remain closed at least until Monday.

Ford expects no effect on its vehicle assembly operations for at least the next several days.