Pneumonia is an in?ammation of the lung tissue (see LUNGS) caused by infection. It can occur without underlying lung or general disease, or in patients with an underlying condition that makes them susceptible.
Pneumonia with no predisposing cause – community-acquired pneumonia – is caused most often by Streptococcus pneumoniae (PNEUMOCOCCUS). The other most common causes are viruses, Mycoplasma pneumoniae and Legionella species (Legionnaire’s disease). Another cause, Chlamydia psittaci, may be associated with exposure to perching birds.
In patients with underlying lung disease, such as CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) or BRONCHIECTASIS as in CYSTIC FIBROSIS, other organisms such as Haemophilus in?uenzae, Klebsiella, Escherichia coli and Pseudomonas aeruginosa are more prominent. In patients in hospital with severe underlying disease, pneumonia, often caused by gram-negative bacteria (see GRAM’S STAIN), is commonly the terminal event.
In patients with an immune system suppressed by pregnancy and labour, infection with HIV, CHEMOTHERAPY or immunosuppressive drugs after organ transplantation, a wider range of opportunistic organisms needs to be considered. Some of these organisms such as CYTOMEGALOVIRUS (CMV) or the fungus Pneumocystis carinii rarely cause disease in immunocompetent individuals – those whose body’s immune (defence) system is e?ective.
TUBERCULOSIS is another cause of pneumonia, although the pattern of lung involvement and the more chronic course usually di?erentiate it from other causes of pneumonia.
Symptoms The common symptoms of pneumonia are cough, fever (sometimes with RIGOR), pleuritic chest pain (see PLEURISY) and shortness of breath. SPUTUM may not be present at ?rst but later may be purulent or reddish (rusty).
Examination of the chest may show the typical signs of consolidation of an area of lung. The solid lung in which the alveoli are ?lled with in?ammatory exudate is dull to percussion but transmits sounds better than air-containing lung, giving rise to the signs of bronchial breathing and increased conduction of voice sounds to the stethoscope or palpating hand.
The chest X-ray in pneumonia shows opacities corresponding to the consolidated lung. This may have a lobar distribution ?tting with limitation to one area of the lung, or have a less con?uent scattered distribution in bronchopneumonia. Blood tests usually show a raised white cell (LEUCOCYTES) count. The organism responsible for the pneumonia can often be identi?ed from culture of the sputum or the blood, or from blood tests for the speci?c ANTIBODIES produced in response to the infection.
Treatment The treatment of pneumonia involves appropriate antibiotics together with oxygen, pain relief and management of any complications that may arise. When treatment is started, the causative organism has often not been identi?ed so that the antibiotic choice is made on the basis of the clinical features, prevalent organisms and their sensitivities. In severe cases of community-acquired pneumonia (see above), this will often be a PENICILLIN or one of the CEPHALOSPORINS to cover Strep. pneumoniae together with a macrolide such as ERYTHROMYCIN. Pleuritic pain will need analgesia to allow deep breathing and coughing; oxygen may be needed as judged by the oxygen saturation or blood gas measurement.
Possible complications of pneumonia are local changes such as lung abscess, pleural e?usion or EMPYEMA and general problems such as cardiovascular collapse and abnormalities of kidney or liver function. Appropriate treatment should result in complete resolution of the lung changes but some FIBROSIS in the lung may remain. Pneumonia can be a severe illness in previously ?t people and it may take some months to return to full ?tness.
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