Tests have confirmed that legionella bacteria was present at the Bulmers cider plant in Hereford, less than a week ago.
Most of the victims are being treated at Hereford County Hospital
The bacteria has been identified in a cooling tower at the company's factory in Plough Lane.
The discovery comes as health officials confirmed another case of Legionnaires' disease, bringing the total number linked to the Hereford area to 23.
A man in his 70s is said to be in a stable condition in hospital.
Herefordshire Council's head of Environmental Health, Andrew Tector, said the tower was closed on 12 November and had been "subject to rigorous cleansing under the supervision of the Health and Safety Executive."
Paul Nicholas, the council's head of food safety, said the discovery of the bacteria posed no risk to the safety of Bulmers' products.
"We have no knowledge of the organism being present in, or transmitted by an alcoholic drink such as cider," he said.
"We therefore have no concerns over the standards of food hygiene at the factory and the safety of the products there."
Dr Brian McCloskey, regional head of the Health Protection Agency, said: "Although we still cannot be certain that the plant on the HP Bulmer site is responsible for this outbreak we have to bear the latest results in mind when looking at the epidemiology of this outbreak."
Seven new cases in the outbreak - which has killed one man - were confirmed on Saturday, with the latest case confirmed on Monday.
The rise marked the biggest increase in the number of cases over 24 hours since the outbreak began.
Health officials said it was not surprising as GPs were on the lookout for symptoms of the disease.
The latest cases include seven men, aged from their 40s to 70s, and one woman in her 50s.
All of the eight, along with the majority of the other infected patients, are said to be stable in hospital.