Randomly select (shuffle the deck and cut it) 2 cards, have the participant with those cards stand, and explain they have caught the flu from the first participant and each will spread it to 2 others. Repeat this process until the card you select is for a standing participant. Explain that you cannot get the flu twice in the same flu season and once you have recovered cannot spread it to others. Select no cards for these standing participants. Eventually, you will select only cards for standing participants, and the outbreak will be over. There should be a few participants still seated, i.e. uninfected. Not everyone gets infected in an outbreak.