The four victims reported high fever, body ache and troubled breathing. Seven other cases have also been identified, from the same clinic where the patients were being treated.

Four people who died under mysterious circumstances in a clinic in the Argentine city of San Miguel de Tucuman were victims of Legionnaires' disease, health officials have confirmed.

Health Minister Carla Vizzotti told reporters that the disease had been identified as the underlying cause of double pneumonia in the recent deaths. They were all suffering from high fevers, body ache and had trouble breathing.

Legionella bacteria causes symptoms ranging from flu to severe lung infection and pneumonia in humans.

The Health Ministry said all the patients belonged to a risk group. They included smokers and people with a history of respiratory disease, obesity, diabetes and high blood pressure.

Other cases identified at same clinic

Seven other symptomatic cases have been identified. All the patients were employees at the clinic where the four eventual fatalities were being treated. Four of them have remained in the hospital, and three were under respiratory assistance at home, with less severe symptoms, said Luis Medina Ruiz, health minister of Tucuman province, on Saturday.

Ruiz had previously said "toxic and environmental causes" could not be ruled out.

Vizzotti said authorities are working to ensure the clinic is safe for patients and staff.

Legionnaires' disease, which was first identified at a 1976 meeting of the American Legion veterans group in the US city of Philadelphia, is caused by contaminated water or unclean air-conditioning systems.

After the outbreak in Tucuman, doctors tested the patients for Covid -19, the flu and hantavirus, which were all ruled out. Samples were then sent to the Malbran Institute in Buenos Aires, where tests confirmed Legionnaires' disease.

Hector Sale, president of the Tucuman provincial medical college, said the infection is not normally transmitted person-to-person, and that no close contact of any of the 11 infected people showed symptoms.