The Aliens in Board learn that one of the Human-Crewmembers has Herpes.
Fact: More than 3.7 Billion People have it. XD -- Anon Guest
"It's my duty to inform my captain and crew that I have a class two plague known as Herpes. I'm on a permanent course of antivirals to prevent its propagation."
Captain Gorthax, mildly alarmed, consulted the free infonets and read, GalStand Medical Primer for Newcomers: Subheading - Plague Disease Classes and resulting mis-assumptions.
Like most numeric classifications, the higher the number, the more 'intense' or 'severe' the classification. Excepting the Esper scale, because Humans concocted it and value numbers in an inverse scale. Attempts to remedy this have been counter-productive. Thusly, it is the exception rather than the rule.