The fourth index case involved Patient #15, a 43-year-old man who was being monitored after having close contact with Patient #4 on the plane. He developed a fever and a sore throat on February 1st and subsequently tested positive. Patient #20, a relative living in the same building but on a different floor, experienced a sore throat on February 4th and subsequently tested positive. It is likely that he was infected whilst eating with Patient #15.