That brings the death toll to 13 since early August, with 177 people infected with the bacteria.
According to the health authority, the latest death involved a patient who had been showing symptoms prior to Aug. 29.
Last week, François Desbiens, the city's director of public health, said "the outbreak is under control because we don't have new cases with the beginning of the disease after Aug. 29."
Health officials said the source of the bacteria is under control because of efforts to sanitize cooling towers in Quebec City's Lower Town.
The lab results obtained from the cooling towers should be made public by mid-October.
The incubation period of the Legionella pneumophila disease lasts between two to 10 days.
After symptoms appears, it takes doctors several more days to diagnose the disease.
The outbreak in Quebec City began in July.