An ARI is an infection affecting the upper or lower respiratory tract that lasts less than 30 days.[1] The upper respiratory tract includes the nose, sinuses, middle ear, pharynx (throat), and larynx (voice box), while the lower respiratory tract includes the trachea and the bronchi, bronchioles, and alveoli of the lungs (the alveoli are where the oxygen and carbon dioxide exchange occurs in the body).
Upper respiratory tract infections are the most common ARIs and include the common cold, sinusitis, tonsillitis, pharyngitis (sore throat), otitis media (ear infection), and laryngitis.[2][3] Lower respiratory tract infections tend to be more serious and include pneumonia, acute bronchitis, bronchiolitis, and bacterial/fungal exacerbations of chronic obstructive pulmonary disease.[3] Some ARIs (e.g., the flu, COVID-19) can affect both the upper and lower respiratory tract, depending on their severity.[4]