Inflammation of the lung, the terminal sections of the air passages, and the tissue in between, usually caused by bacteria or viruses, sometimes by a fungus. In the alveoli, oxygen is removed from inhaled air and replaced with carbon dioxide. In pneumonia inflammation cells and fluid accumulate, with the result that the alveoli cannot fill properly with air, making the process of breathing difficult. The cause of the disease reaches lung tissue in inhaled air, or via the blood from an inflamed area elsewhere in the body. In the presence of factors that increase the risk of pneumonia it can be advisable to vaccinate the patient against influenza; this is particularly important for older people or chronic bronchitis and asthma sufferers. Inflammation can also occur (obstruction pneumonia) if a branch of the air passages is constricted by a tumour, inflammation or a foreign body (a peanut, for example). Aspiration or swallowing pneumonia can occur through the inhalation of pus or a piece of inflamed tissue, after a tonsillectomy for example. Disorders in the swallowing process can also cause this form of pneumonia. The first signs of pneumonia are often cold shivers and a rapid rise in body temperature. If the source of infection is a virus, pneumonia is usually preceded by a cold or influenza. A mixture of pus and mucus forms in the lungs as a result of the inflammation reaction, and this is coughed up as sputum which is clear, yellowish-green or rust-brown according to the cause of the illness; it can also contain pus or blood. Local irritation of lung tissue can occur, causing pain in the side or chest, particularly when the patient breathes deeply or coughs. In cases of infection with certain bacteria, cold sores often occur at the same time. Pneumonia is treated with antibiotics, and the patient usually recovers within two to three weeks. Regular knocking on the chest helps in coughing up the sputum; sometimes excess pus has to be removed by suction. A rise in the patient’s temperature during treatment suggests a complication such as pleurisy, empyema or sepsis (blood poisoning). It is customary to perform laboratory tests on blood and expectorated sputum in cases of pneumonia. If complications occur, further tests are necessary, such as bronchoscopy, CAT scan of the chest, or bronchography (contrast X- rays of the air passages).