Gillian Beckingham, 46, was in charge of the upkeep of the air-conditioning system at the Forum 28 arts centre in Barrow, Cumbria, when it spewed deadly bacteria into the air, Preston Crown Court heard.
Six women and one man died and a further 172 people were infected during the outbreak in July and August 2002.
Beckingham, a married mother from Grange-over-Sands, Cumbria, denies the unlawful killing of Richard Macauley, 89, Wendy Milburn, 56, Georgina Somerville, 54, Harriet Low, 74, Elizabeth Dixon, 80, June Miles, 56, and Christine Merewood, 55.
Beckingham, who was born in York and trained at the School of Architecture in Leeds, also denies breaching health and safety laws.
The jury of eight women and four men retired at 10.10am yesterday (19 April) to continue considering its verdict after six hours of deliberation.
Barrow Borough Council, which owns Forum 28 and employed Beckingham as its head of design services, has already pleaded guilty to breaching the Health and Safety At Work Act, but was cleared of manslaughter midway through the trial.