Flu

"You'd better get out of here, Harry. Filch isn't in a good mood — he's got flu and some third years accidentally plastered frog brains all over the ceiling in dungeon five. He’s been cleaning all morning, and if he sees you dripping mud all over the place —"

- Nicholas de Mimsy-Porpington to Harry Potter in the autumn of 1992.

Flu is an acute contagious disease of the upper airways and lungs, caused by a virus, which rapidly spreads around the world in seasonal epidemics. The most common symptoms of the disease are chills, fever, sore throat, muscle pains, severe headache, coughing, weakness/fatigue and general discomfort.

In late October, 1992, Argus Filch got the flu, and as a result, walked about wheezing and wild-looking, with a thick tartan scarf around his head, and his nose unusually purple. In September, 1993, Sybill Trelawney predicted classes would be interrupted in the following February due to a nasty bout of flu, in which she would lose her voice herself, which appeared not to correspond with what really happened.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Prisoner of Azkaban