Inflammation of 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), BRONCHIECTASIS, and CYSTIC FIBROSIS, other organisms such as Haemophilus influenzae, 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) can be fatal.
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 can cause disease in individuals whose immune system is effective.
TUBERCULOSIS is another cause of pneumonia, although the pattern of lung involvement and the more chronic course usually differentiate it from other causes of pneumonia.
There may be no or few symptoms initially but, as the illness progresses, cough, fever (sometimes with RIGOR), pleuritic chest pain (see PLEURISY) and shortness of breath develop. SPUTUM may not be present at first 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 filled with inflammatory 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 (see FREMITUS).
The chest X-ray shows opacities corresponding to consolidated parts of the lung. This may have a scattered distribution when it is often described as bronchopneumonia or a distribution fitting with limitation to one section of the lung (lobar pneumonia). Blood tests usually show a raised white cell (LEUCOCYTES) count. The organism responsible for the pneumonia can often be identified from culture of the sputum or the blood, or from blood tests for the specific ANTIBODIES produced in response to the infection.
This involves appropriate antibiotics together with oxygen, pain relief and management of any complications that may arise. When treatment is started, the causative organism may not yet have been identified so that the antibiotic choice is made on the basis of the clinical features, knowledge of 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 effusion 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 fit people and it may take some months to return to full fitness.