Avoiding close contacts with infected people could not be enough as a defense against flu. This is the conclusion of a recent study by scientists at the Wake Forest School of Medicine, published on the Journal of Infectious Diseases. The swab specimens of 94 subjects, admitted to the hospital with influenza-like illness, have been analyzed and their medical history recorded, revealing that 61 of them were actually positive for flu. Researchers then collected air samples from each patient, looking for infectious particles. This allowed to discover that 26 of them released virus particles into the air, with 5 being highly infectious, emitting up to 32 times more virus than others. Patients who reported severe illness and major interference with daily life also emitted more influenza virus.
Most of all, virus particles have been found in air samples even at 6 feet from the patients, a result that seems to question the current paradigm of localized droplet transmission at short distance through coughing or sneezing. Thus, the conventional wisdom that flu is mainly spread through close contact with others and by touching contaminated surfaces could be wrong.

http://jid.oxfordjournals.org/content/early/2013/01/29/infdis.jis773.abstract