The first four cases of legionnaires' disease were announced on Sunday.

In a statement released on Monday morning, the DGS said that six cases of legionnaires' connected to the CUF Descobertas hospital had been diagnosed. The patients are five women and one man and they are in a stable condition, according to the statement.

Legionella is the bacterium responsible for legionnaires' disease, a form of severe pneumonia that usually begins with dry cough, fever, chills, headache, muscle aches and difficulty breathing. There may also be symptoms of abdominal pain and diarrhoea. The incubation period if five to six days after infection, and may be up to 10 days.

The infection is contracted by breathing in infected water droplets or by aspiration of contaminated water. Although severe, the infection has effective treatment.

An outbreak of legionnaires' disease in Vila Franca de Xira in November 2014 caused 12 deaths and infected 375 people with the bacteria.

This outbreak, considered the third largest in the world, started on 7 November and was controlled in two weeks. The health minister at the time, Paulo Macedo, stressed that hospitals had “treated more than 300 patients with pneumonia."