Germs are invisible bacteria, particularly prevalent in the first ten levels of the Caverns of Creation. They become exceptionally rare (a 1 in 50 chance) on subsequent levels. The game never spawns more than one germ in a single level, except for prime-numbered levels, which will always spawn two.
Germs are stationary, invincible, and invisible. At base they do an unavoidable 3 points of damage to any creature standing on their square and two points to any creature in adjacent squares. Germs have a 1 in 10 chance of infecting creatures on their square and a 1 in 20 chance for creatures adjacent. Exceptions: creatures made of limestone are immune to germs, though they can carry an infection, and cursed creatures born in the Year of the Rabbit, which recieve double damage and have an increased chance (2 in 3) of infection.
Infected creatures are dealt 1 point of damage for every round that they are infected, up to eight rounds; any creatures (including the player) in squares adjacent to an infected creature is dealt 1 point of damage and has a 1 in 6 chance of being infected themselves.
"The [name of monster] coughs" or "You hear wheezing" is a tell-tale sign of an infected monster, and thus the presence of a germ on the level. Because germs cannot be seen (and have no symbol), the only way for players to detect them is through deductive reasoning.