Legionnaires' Disease - Renfrew area
NHS Greater Glasgow and Clyde (GGC) said the new case was responding well to treatment at home and has not required hospital treatment.
The previous five cases, which were also in the Renfrew area, have all recovered and left hospital.
The health board and Health and Safety Executive are continuing investigations into the source of the outbreak.
Dr Gillian Penrice, NHS Greater Glasgow and Clyde's consultant in public health, said: "Given the two week incubation period of the disease it was always a possibility that some further cases may be identified.
"I am pleased however that this individual has a mild form of the disease and is responding well to treatment at home."
Dr Penrice added: "We have notified all community GPs and our frontline hospital teams to keep this outbreak uppermost in their minds when dealing with patients displaying symptoms of headache, fever, dry cough, breathing difficulties, stomach pains and diarrhoea."
Anyone with these symptoms is urged to contact NHS 24 or their own GP.