According to the Centers for Disease Control and Prevention, the flu is highly contagious, and it does not need physical contact to spread from person to person. It is possible to contract the flu by breathing in active virus particles that are expelled when an infected person coughs, sneezes or speaks.
The CDC explains that even healthy-looking people can spread the flu, as most individuals become contagious before they start showing flu symptoms. Flu-infected individuals are usually contagious for at least a week, though children can be contagious for more than a week. During this time, those infected with the flu must minimize contact with others, stay home, and avoid sharing bedding, food, utensils, clothing and other household objects with others.