About 2,500 employees returned to work last week at a Ford Motor Co. engine parts plant near Cleveland. It was shut down for five days due to a deadly outbreak of Legionnaires’ disease.

The source of the disease still is not known, although some suspect the plant’s cooling towers. "We do not know that it was the cooling towers," says Della DiPietro, a Detroit-based Ford spokesperson. Regular maintenance is performed on the towers two times each year, she says.

The March 20 reopening of the 49-year-old Cleveland Casting Plant in Brook Park, Ohio, follows an investigation and cleanup process that involved health officials from local, state and federal agencies, including the Centers for Disease Control, Occupational Safety and Health Administration, Ohio Dept. of Health and Cuyahoga County Board of Health.

The disease has been confirmed in four plant employees. Two of them, Donald Tafoya, 61, and David Hinderman, 53, have died. Three more workers have pneumonia, but they have not yet been diagnosed with Legionnaires’ disease.

Officials involved in the investigation say that it would be premature to identify suspect areas since results from 157 biological samples collected at the plant by Ford and the CDC will not be available for several days. "It takes time to grow [the cultures] and analyze the samples," says Rob Medlock, OSHA Cleveland Area Director. "It is still too early to identify the source."

Legionella was first identified 24 years ago after 34 attendees of an American Legion Convention in Philadelphia died of pneumonia. It is an airborn bacteria that can grow in any area where tepid water has an opportunity to stagnate. Common sources of legionella include air conditioning systems, cooling towers, humidifiers and even showers.

The bacteria can cause an infection that has two distinct forms, according to Michael Goodman, a physician and managing scientist at Exponent, a Menlo Park, Calif.-based scientific research firm. The more severe illness is Legionnaires’ disease, which includes pneumonia. The more mild sickness is Pontiac Fever, a flu-like illness, says Goodman. The infection cannot be passed from person to person.

Novi, Mich.-based Clayton Group Services Inc., an environmental safety consulting firm, supervised the three-day cleanup process performed by hourly and salaried Ford employees.

The decontamination included disinfecting the plant’s equipment, mechanical systems and water systems with chlorine or superheated water. "Every area that had a potential for the bacteria to proliferate was disinfected," says John McLeod, assistant director of the environmental health division of the Cuyahoga County Board of Health. A maintenance program developed by Ford will be monitored by the county and OSHA.

Ford will be stepping up maintenance and testing at all plants to prevent a reoccurrence. "We have a plan and we are committed to it," says Roman Krygier, Ford vice president for powertrain operations.

Because it is difficult to distinguish Legionnaires’ disease from other forms of pneumonia, many cases go unreported. Between 8,000 and 18,000 people contract Legionnaires’ disease in the U.S. every year, according to estimates by Atlanta-based CDC. Between 5 and 30% of those who contract the illness die, say CDC officials.

Because legionella is so common, health officials have not ruled out sources for the bacteria outside the plant. "If you look for legionella, you will find it. It is out there," says Jay Carey, public information officer for the Ohio Dept. of Health.

"Legionella is ubiquitous," agrees McLeod, calling the Ford outbreak a "wake-up call."