Inflammation of the parotid gland. Acute bacterial parotitis is characterized by redness, pain, tenderness, and swelling over the affected gland, often with a discharge of pus from the opening of the parotid duct on the inside of the cheek. It may occur following radiotherapy or in patients with a compromised immune system; treatment is with antibiotics and pain relief. Infectious parotitis (mumps) is caused by a viral infection of one or both parotid glands. Chronic recurrent parotitis is characterized by discomfort and repeated swelling of the parotid gland frequently after eating; it is associated with a decreased flow of saliva, often due to a narrowing of the parotid duct or blockage by a salivary stone. Less common causes of parotitis are actinomycosis and Sjögren's syndrome.