Most experts believe that influenza is transmitted (up to 6 feet) from an infected person’s cough or sneeze. Virus-laden respiratory droplets from an infected sneeze can be inhaled through the nose or mouth of nearby persons. These respiratory droplets only remain suspended in the air a few seconds and then settle on environmental surfaces where they remain viable for minutes to hours. A less common method of transmission is when a person touches a contaminated environmental surface and then inoculates their eye/nose/mouth with the virus. For these reasons, it is important to use proper respiratory etiquette with all coughs/sneezes, as well as proper hand washing precautions.
Once the virus enters the body, it usually incubates 2-3 days before clinical symptoms develop. Adults can shed influenza virus from the day before symptoms begin, but are most contagious the first 3-5 days of clinical illness, with most shedding complete by day 7. Children and immunocompromised adults can shed the virus ≥ 10 days.