Flu is a respiratory disease caused by the influenza virus which infects human cells through the air, sharing utensils, or direct contact. Flu symptoms include fever, fatigue, loss of appetite, sore throat, dry cough, nausea, and burning eyes. Treatment involves rest, eating nutritious foods to boost the immune system, and antibiotics if bacterial infections occur as indicated by discolored nasal mucus or a hoarse painful throat. To prevent flu, people should wash hands, rest, eat healthy foods, exercise, quit smoking, avoid biting fingers, sneeze properly, and smile.