Symptoms of the flu usually last for seven to 14 days, with the individual being contagious beginning a day before symptoms appear through the first week of the flu, according to Flu.gov. Young children and adults with weakened immune systems sometimes remain contagious longer.
The influenza virus causes the flu, according to MedlinePlus. It spreads in the droplets of water that form when an infected individual coughs or sneezes. People also catch the flu by touching surfaces with the virus on them and then touching their eyes, nose or mouth. After exposure to the flu virus, many people begin to experience symptoms within one to seven days.
The flu often spreads rapidly within groups, reports MedlinePlus. Once it arrives in a school, students get sick within two to three weeks. A high fever, between 102 and 106 degrees Fahrenheit, is often the first sign of the flu. Other symptoms include body aches, headaches, chills, dizziness and a lack of energy. While the flu is primarily a respiratory disease, some patients also experience nausea and vomiting.
When a person has the flu, MedlinePlus recommends he remain in his home for at least a day after his fever ends. It also recommends frequent use of hand sanitizer and avoiding the sharing of utensils, bottles and cups. The use of tissues to cover a cough or sneeze also prevents the spread of flu germs.