The contagious period for an upper-respiratory tract infection varies according to the specific infection and the cause of that infection. The common cold, the most common form of upper-respiratory infection, is most contagious during the first two or three days that a person exhibits symptoms, according to MedlinePlus. Someone with the common cold virus rarely is contagious after one week.
The upper-respiratory tract refers to the pathway that carries air to the lungs and includes the nose, sinuses, throat and larynx, states the American Rhinologic Society. An upper-respiratory tract infection usually refers to acute viral rhinitis, or the common cold.
The cold virus is transmitted from an infected person to others through sneezes, coughs or touching something contaminated by the virus, states WebMD. Viruses such as those that cause the common cold can remain on surfaces for up to a few hours, and bacteria, a common source of many upper-respiratory infections, can remain on surfaces for up to three days.
Other upper-respiratory tract infections include sinusitis, laryngitis and strep throat. A strep throat is caused by airborne bacteria spread through an infected person's breathing, coughing or sneezing, according to WebMD. Typically it is contagious from three to five days before symptoms appear in the infected person. Strep throat is contagious until 24 hours after the infected person begins an antibiotic.