When they find out what venue, if any, they have in common, They’ll be better able to pinpoint what happened.
A few years back we were on a 7 day cruise on Royal Caribbean. About 5 days in, There was a similar sized outbreak. It turned out that the hundred people affected had all stepped ashore On Haiti and had sampled their wares. Not one of your better ideas. The trip was cut short by one day and we missed Montego Bay on Jamaica. Believe it or not, we were completely comped. So because of that outbreak we got a 6 day cruise for nothing. Silver linings.
They were so weak, they couldn’t even brawl at the baggage claim.