When I was at University, the second and third weeks of the semester immediately after Christmas were notorious for widespread illnesses. All the students would reconvene after spending a month back home in their parental homes all across the country. They would socialise with their friends from their pre-student days, and be exposed to the various regional strains of coughs, colds and flu. This pretty much guaranteed that when we reassembled on campus everyone would be exposed to strain of virus from some part of the country that they had not seen before and had no immunity. And once the incubation time was over, the coughing would commence.
This basic recipe can be improved upon. Travelling by air provides an opportunity for an individual traveller to spend several hours with a few hundred random strangers in a small volume with recirculating air, plus time hanging around at airports with several thousand more. The more legs and stopovers on the journey, the better for a multiplier effect. A bit of local tourism along the way adds a concentrated expose to local strains.
So assemble fifty or so people together from random parts of the world, and have them fly in. Then confine them in a small volume for several weeks, eating together and sleeping in cramped shared rooms, and watch the snuffles begin.
The Europa on this Antarctic voyage improves still further on this recipe, with even the permanent crew having flown in to join the ship in Montevideo (or at least all bar two who are presumably there to provide a conduit for the viruses of the previous voyage crew). Viruses target people who are tired, hungry and run down, so introduce night watches to deprive people of sleep, and throw in a nice rocking motion to get people seasick to drive up infection rates. And since the general advice for viruses is rest, warmth and food, head south to turn the midnight watches into freezing midnight watches and turn the rocking motion into a severe rocking and lurching motion to get more sea-sickness.
At the halfway point the surprising thing is not that the Europa is a plague ship, but that it is not drifting in the Southern Ocean with nobody at the helm and just the sound of groans and coughs and splutters from below with the occasional splash as yet another victim is consigned to the deep by the barely living. Maybe it is the nightly cleaning by the hardworking crew as they wipe down and disinfect every surface in the ship which is keeping the ship sailing after all. (The awesome galley would of course be unaffected, but getting more and more despondent as the number of people capable of eating their offerings dwindles. Eventually they would realise that they were the only people left and with supplies running low, they would sail the ship to the nearest port for re-provisioning and re-crewing. Which they would of course do perfectly with favourable winds, an escort of dolphins, albatrosses and a couple of blue whales. And of course an endless supply of delicious soups.)
With this enhanced virus propagation strategy in place it is highly likely there is more than one patient zero, and that these reprobates have covered their tracks by picking up a second viral infection to
avoid the guilty signs of being the one of the few healthy people two weeks into the trip. To add to our misery we are deprived of the ability to play the blame game.
The Doctor reads the Riot Act in the evening, reminding people that basic hygiene has moved on significantly since the ship was built, and maybe we should follow. Cough into your elbow and not your hand (and certainly not into the atmosphere unconstrained). Wash hands before eating. The short forks for picking cheese and ham may not be ideal, but they are better than no forks (and particularly coughing into a hand and then using the same hand to pick up food directly). But the audience is lacking many of the more pestilential people who are coughing noisily in their cramped cabins, and the bad habits continue.