CHAMBERSBURG, Pa. (AP) _ A hospital may be one of several sources of Legionnaires' disease that has killed three people in the biggest outbreak since 1976.

The victims all died in the last week, the latest on Tuesday. Ten others are known to be infected with the disease, which is transmitted in airborne water droplets, often through air-conditioning systems. Test results were pending on 30 to 50 more people.

Federal health officials found that some of the sick had been in Chambersburg Hospital _ as employees, volunteers, patients or visitors _ before the outbreak.

The federal Centers for Disease Control and Prevention is still testing water samples from the hospital. It has since flushed its hot-water system with 170-degree water and sanitized its air-conditioning system, hospital President Norman Epstein said.

In Cloquet, Minn., a Carlton County office building was closed indefinitely after the bacteria that causes Legionnaires' disease were found in the building's hot-water heater, said Larry Sundberg, an epidemiologist for the St. Louis County Health Department.

He said one worker has contracted the illness, but the source has not been determined.

The building's air-conditioning system malfunctioned June 20, leaking water where mold and mildew later formed. The building, which houses the state Department of Motor Vehicles and other offices, was closed soon afterward.

Legionnaires' disease derived its name from an outbreak in 1976, when 29 people attending an American Legion convention at a Philadelphia hotel became infected and died.

Symptoms usually do not appear for two to 14 days and infected people can die within days if not given antibiotics.