For how long?
How long it takes for a droplet infection to cause symptoms varies depending on the type of pathogen. The time between the absorption of the pathogen into the body and the onset of the disease is called the incubation period. In case of a flu-like infection, the incubation period is about two to five days.
However, carriers of the pathogen are usually contagious one day before the first signs of the disease appear. How long the disease itself lasts, depends on the particular disease. A flu-like infection should be cured after about one to two weeks.