Streptococcus pneumoniae is the most common cause of pneumonia worldwide, and pneumonia is the most common manifestation of pneumococcal infection, being present in 68% of cases of pneumococcal bacteraemia in a study by Balakrishnan etal. (2000). Pneumococcal pneumonia is estimated to affect 1 in 1000 adults each year (World Health Organization, 1999). Disease occurs when body defences fail to prevent pneumococcal access to and subsequent replication in the alveoli.
The most frequent clinical picture is an ill patient who reports sudden onset of fever in association with pleuritic chest pain and other nonspecific symptoms such as headache, vomiting and diarrhoea. Cough soon develops, which is initially dry but often followed by haemoptysis. The presentation may be much more subtle in elderly and immunocompromised patients. Physical examination reveals signs consistent with consolidation. Pleural effusion may also be detectable. These findings are confirmed by chest X-ray, which usually shows consolidation filling all or most of a lobe. S. pneumoniae is not a classic abscess-producing organism, and lung abscess should raise suspicion of other pathology such as bronchial obstruction or pulmonary infarction. Most patients with pneumococcal pneumonia have a leucocytosis. Some patients, however, have a low leucocyte count, which indicates a very poor prognosis (Balakrishnan etal., 2000). Abnormal liver function tests are also a common finding.
The presence of abundant neutrophils together with lanceolate Gram-positive diplococci in sputum strongly suggests the diagnosis, which is usually confirmed by microbiological culture of respiratory tract specimens (most often sputum) and blood.
The case fatality of pneumococcal pneumonia approximates 5-10% and increases to 20% in the presence of bacteraemia. Besides the bloodstream, infection can rarely extend to involve the pericardial and pleural cavities, resulting in empyema.
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