"Most healthy adults may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. People with flu can spread it to others up to about 6 feet away. Flu viruses are spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs," according to the CDC.
People can also catch the flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose. Studies have also shown that human influenza viruses can survive on surfaces between 2 and 8 hours.
All of this infection adds up to a significant economic cost as researchers cite direct costs due to lost productivity from colds at $25 billion in the U.S. Taking into consideration both indirect (lost productivity) and direct (doctor visits and medicine) costs, of colds, the figure in the U.S. annually is $40 billion. Flu prevention is actually very good for business.