Indeed. My thought was that CO2 levels could roughly correspond to the number of people in the specific room, offset by actual ventilation levels.
IE more CO2 = more risk because it means more people with inadequate ventilation.
Conference crud is really simple. Hacker or not. You bring in hundreds/thousands of people from around the country and world, exposing most of them to even more potential disease carriers on airplanes, trains, busses, and more, then disrupt people's sleep and disgestive tracts with unfamiliar locations, schedules and food and you have the perfect melting pot to get people sick.
What can be done to help prevent it? Mask wearing might help some, along with sanitary other stuff - improve the ventilation in such buildings, including good filters, UV lights and such helping to sterilize the air. At the same time, improve air quality otherwise, because harsh cleaning chemicals can also make people sick.