How Flu Spreads

Person to person is the main way that influenza viruses can spread. Usually it spreads by respiratory droplets of coughs and sneezes. This can happen when droplets from cough or sneeze of an infected person are propelled through the air and deposited on the mouth or nose of people nearby. Influenza viruses may also be spread when person touches respiratory droplets on another person or an object and then touches their own mouth or nose, or even someone else's mouth or nose before washing their hands. Also flu is catching. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5-7 days after getting sick. Symptoms start 1 to 4 days after the virus enters the body. That means that you can pass on the flu to someone else before you know you are sick, as well as while you are sick. Some persons can be infected with the flu virus but have no symptoms. During this time, those persons may still spread the virus to others. In addition, linens, eating tools, and dishes belonging to those who are sick should not be shared without washing thoroughly first and individuals should avoid any laundry before washing it to prevent contaminating themselves. And it is very important that eating tools are washed either in dishwasher or by hand with water and soap.

http://www3.niaid.nih.gov/topics/flu/understandingflu/howfluspread.htm