The upper respiratory tract includes the sinuses, nasal passages, pharynx, and larynx. These structures direct the air we breath from the outside to the trachea and eventually to the lungs for respiration to take place.An upper respiratory tract infection, or upper respiratory infection, is an infectious process of any of the components of the upper airway.Infection of the specific areas of the upper respiratory tract can be named specifically. Examples of these may include rhinitis (inflammation of the nasal cavity), sinus infection (sinusitis or rhinosinusitis) - inflammation of the sinuses located around the nose, common cold (nasopharyngitis) - inflammation of the nares, pharynx, hypopharynx, uvula, and tonsils, pharyngitis (inflammation of the pharynx, uvula, and tonsils), epiglottitis (inflammation of the upper portion of the larynx or the epiglottis), laryngitis(inflammation of the larynx), laryngotracheitis (inflammation of the larynx and the trachea), and tracheitis (inflammation of the trachea).Upper respiratory infections are one of the most frequent causes of doctors visits with varying symptoms ranging from runny nose, sore throat, cough, to breathing difficulty, and lethargy. In the United States, upper respiratory infections are the most common illness leading to missing school or work.
Although upper respiratory infections can happen at any time, they are most common in the fall and winter months, from September until March. This may be explained because these are the usual school months when children and adolescents spend a lot of time in groups and inside closed doors. Furthermore, many viruses of upper respiratory infection thrive in the low humidity of the winter.