pneumonitis /no̅o̅′mənī″tis/ pl. pneumonitides [Gk, pneumon + itis] , inflammation of the lung. Pneumonitis may be caused by a virus or may be a hypersensitivity reaction to chemicals or organic dusts, such as bacteria, bird droppings, or molds. It is usually an interstitial, granulomatous, fibrosing inflammation of the lung, especially of the bronchioles and alveoli. Dry cough is a common symptom. Treatment depends on the cause but includes removal of any offending agents and administration of corticosteroids to reduce inflammation. Compare pneumonia.