Well, it's entirely possible.
A highly contagious thing gets on a closed system of closely packed people, and it can spread like wildfire. Serious flus and plagues have spread like wildfire in very open areas.
In any case, it is not encouraging. Makes you wonder what disease-ridden person you're getting on board with who'll knock everyone flat.
Sort of like the Staph infections that have become the scourge of hospitals.