Grandmother Norma Bigi, 84, the latest victim of the illness, died after tests revealed the bacteria came from water from a fountain in Bresso, a town near Milan.
Those taken ill from the disease found themselves suffering its classic symptoms in the past 12-13 days and have all been admitted to hospital while authorities make attempts to control the outbreak.
Simone Cairo, mayor of Bresso, said: “The situation is under control, all the authorities that had to take action have been activated.
“This morning, the mayor of Milan Giuseppe Sala called me to give us support, let’s see how he can help us.”
He went on to say most of the patients battling the condition have been discharged from hospital.
Tests revealed the bacteria also found its way into the home of one person infected as well as via the route of the water fountain.
For four years the disease has been absent from the region but its shock return has sparked terror in from Brest residents.
Other victims who have since died from the outbreak are Lino Mazzola and Eden Stocchi, both 94.
All three died at the Cinisello Balsamo hospital.
Mr Cairo has taken it upon himself to close four of the town’s fountains as well as the garden of Lino Mazzola following reports the deceased sat there every day.
Mr Cairo also demanded surveys of the air to be done, leaving no stone unturned.
The last time to town suffered a legionella outbreak was in 2014 when between January and September nine people lost their lives after becoming infected.
Sadly, authorities were unable to find out where the bacteria came from during that outbreak.
Italy has acquired the highest cases of legionella disease in all of Europe, with Germany, France and Spain following close behind.
Between 2011 and 201,5, Italy was responsible for up to 1535 cases of legionella according to a report from the European Centre for Disease Control (ECDC).
Migration, climate change and air purifiers are common causes of the illness.
Symptoms include a cough that may brig up mucus or blood, shortness of breath, chest pain, nausea, vomiting, diarrhoea and confusion.