Except Legionaire's Disease is spread through the air conditioning/ventilation system so it doesn't make any difference if a cabin is used or not. The air is always on.
the bacteria spreads through mist, such as from air-conditioning units for large buildings.
Not just HVAC systems. It can spread through things like showers, water jets of hot tubs, and other things. Such as "Unoccupied Floors or Rooms – Low occupancy decreases water flow, which can decrease disinfectant levels and increase the risk of Legionella growth."
Some CDC info about "Reopening Buildings After Prolonged Shutdown or Reduced Operation: Ensure the safety of your occupants and building water system and devices: Check for hazards including Legionella, mold, and lead and copper." https://www.cdc.gov/nceh/ehs/water/legionella/building-water-system.html and "Considerations for Hotel Owners and Managers: How to Prevent Legionnaires’ Disease" https://www.cdc.gov/legionella/wmp/hotel-owners-managers.html
Captain Kate McCue of the Celebrity Edge did a video during shutdown when they had minimal crew on board. It showed one of the daily tasks that had to be done and how they did it: they had to go to every single stateroom on board and run all the taps and showers for a minimum time and flush all the toilets. It all had to be documents. This was to prevent things like Legionella. As you can imagine, time consuming, but it was neat seeing the system they had worked out to do it. And yes, on some days, the Captain did the task work too.
SW