Illness is a card contained only in Tanto Cuore (Base Game)
"In your Starting Phase: You may discard a '3 Love ' card from your hand. If you do, return this card to town."
Cost: 4 Love
Illnesses are most frequently used to disable opponents' Private Maids . This is most effective early in the game, before players are likely to have "3 Love" cards to heal their PMs with. Illnesses can also be used to disable opponents' Chambermaids to deprive them of VP, but this is best done in the last few rounds, so that your opponents will not have time to cure the Illness.
Employing Claire Saint-Juste and Sora Nakachi can also help you cure or prevent Illnesses, if they are available.