Another 292 people have been hospitalized with pneumonia-like symptoms that indicate they may have Legionnaires' disease, health counselor Francisco Marques said.
On Tuesday, 86 people had been diagnosed with the illness. Sanitation crews using chlorine worked Wednesday to disinfect four air conditioning systems found to be lodging the bacterium that causes the disease, although it is not yet known if any of them is the actual source of the outbreak.
One system is located in the city's largest department store. Health investigators believe all the victims lived, worked or passed through two downtown neighborhoods of Murcia, some 400 kilometers (250 miles) southeast of Madrid.
Legionnaires' disease, a form of pneumonia, was identified after an outbreak that killed 34 people at a 1976 American Legion convention in Pennsylvania.
The bacterium that causes it is typically spread when contaminated water is released into the air through air conditioners, steam or other means.
Symptoms include headache followed by high fever, shortness of breath and abdominal pain. On Sunday, a 65-year-old man believed to have the disease died, but officials would not confirm the cause of death.