Gillian Beckingham, 48, is accused of failing to provide for the maintenance of an air conditioning unit at a council-run arts centre in Barrow, Cumbria.
Her trial at Preston Crown Court heard how, in summer 2002, the unit at Forum 28 was the source of an outbreak of the deadly disease.
Six women and one man died after contracting the disease and around 172 others were infected - and many left permanently invalided.
Beckingham was head of the design services group at Barrow Borough Council and it was her responsibility, the prosecution claims, to ensure the unit was properly maintained.
Alistair Webster, prosecuting, told the court Beckingham cancelled a contract which provided for the necessary upkeep of the unit.
After months of neglect it became a perfect breeding ground for bacteria, he told the court.
During July and August 2002, passers-by noticed clouds of mist being emitted from the building into an alleyway linking Barrow market with its bus station. Many fell ill soon afterwards and some never recovered.
Beckingham told the court she had received no health and safety training from the council and other members of staff were responsible for the air conditioning unit.
Beckingham denies the manslaughter of Richard Macauley, 88, Wendy Milburn, 56, Georgina Somerville, 54, Harriet Low, 74, Elizabeth Dixon, 80, June Miles, 56, and Christine Merewood, 55, all from Barrow. She also denies breaching health and safety laws.
Judge Burnton told the jury he would ask them to consider verdicts on the health and safety charge and five of the manslaughter charges.
Depending on those verdicts, the jury might then return to court for a summary of evidence relating to two further manslaughter charges, he said.
The defence disputes whether Legionnaires was the principal cause of the two deaths that relate to these charges.