Unfortunately, I did not have any good way to publicize the survey. Some people answered it who heard about it in one way or another, while I have no way to know how many people never heard of it. The total number of people who answered the survey and said they got sick was 26. One person got sick somewhat later and did not have the classic symptoms of norovirus. The other 25 had symptoms and timing consistent with norovirus, but of course there's no way to be sure what disease they had. One person said they thought they had caught the virus before even going to the con. So all I can say is that 24 or more people probably got norovirus at Arisia. It might be only 24; it might be many more.
Of the 3284 people who attended Arisia 2012, how many would we expect to get sick with norovirus just from the general prevalence of the disease? According to the CDC, something like 6% of Americans get norovirus in any given year. If there were no seasonality, about 0.08% of people would get sick in any 5-day period. In fact, while norovirus occurs all year it is more common from October through March. Furthermore at the time of Arisia there was higher prevalence in Boston, but I have not been able to find out how high. If we take 0.08% of 3284 we would expect only 2 or 3 people getting sick. Even with enhancing factors, I suspect that even 24 cases cannot be just explained by chance (and I also suspect the real number to be significantly higher than 24). So I think this virus was being passed from one person to another at Arisia more than in the population at large.
I asked people where they ate during the con. Out of 24 people who got sick, 20 ate at the Con Suite. Probably most people who go to a con eat something at the Con Suite, so I don't think it is of any particular significance that 5/6 of those who got sick did so. Of more interest is that 4 people who did not eat there got sick anyway. Of the 24 people, 16 ate at M.J.O'Connor's. No other place was listed by as many as half the 24.
I'm not an epidemiologist, but here's my opinion. I don't think this sounds like the kind of outbreak that you get from poor sanitation in food service. In such a case I would expect all the people who got sick to have eaten some specific batch of food. The pattern here seems more like a few attendees had the virus and infected others.
Procedures that I observed in the Con Suite and Green Room seemed well designed to prevent food servers from passing on diseases to patrons. However, food presentation was not well designed to prevent patrons from giving diseases to each other. There was food on trays and in bowls (without serving utensils) where a person picking up one item could easily touch others. There were bags of chips with openings clearly designed for pouring the chips out, but in fact people were reaching into the bags. I think the food presentation should be arranged with the understanding that most people don't think about sanitation at all and won't behave in a safe manner unless they have no choice.
My thanks to everyone who filled out the survey.
Feel free to contact me at kdo@cosmos.phy.tufts.edu.