The outbreak has been traced to the water distribution system at the 146-bed Veterans Administration Pittsburgh Healthcare System University Drive Campus in Oakland, Pa., the Pittsburgh Tribune- Review said Thursday.
Hospital officials said last week four patients who developed pneumonia caused by the Legionella bacteria were successfully treated and released.
VA spokesman Dave Cowgill declined to offer specific information on the fifth patient, citing federal privacy laws, but told the newspaper the patient likely contracted the illness before officials finished cleaning the hospital's water system by hyperchlorination and flushing.
The hospital has imposed water restrictions since the outbreak began Nov. 16, and officials have brought in bottled water for drinking and bagged water for bathing, the newspaper said.
Officials determined the fifth patient was infected at the hospital, basing the conclusion on the incubation period for the bacteria, about 14 days, Cowgill said.