Streptococcus pneumoniae

Streptococcus pneumoniae was identified as a major respiratory pathogen shortly after its isolation in 1881.1 Despite a century of intensive study, and antibiotics which readily kill the organism, respiratory tract infections caused by the pneumococcus remain a formidable problem.S pneumoniae is the commonest cause of community acquired pneumonia, accounting for up to 70% of cases in hospital.2 3 Pneumococcal pneumonia is associated with bacteraemia more frequently than other bacterial pneumonias4 and mortality from bacteraemic pneumococcal pneumonia during the first few days of hospitalisation has changed little since the pre-antibiotic era.5 6 There is also evidence, from the UK and other countries, that the number of cases of pneumococcal bacteraemia is rising.7 8 In the third world five million children under the age of five die each year from acute lower respiratory tract infections in which S pneumoniae is probably the primary agent,9 and patients with HIV infection and AIDS also have a high risk of pneumococcal pneumonia and bacteraemia.10 Furthermore, the worldwide increase in penicillin resistance among pneumococci11-15 and the limited use of the pneumococcal vaccine16 suggest that morbidity and mortality from pneumococcal disease may increase.

In recent years there has been an increased understanding of the interactions between the pneumococcus and the host, both in terms of how the virulence factors of the organism contribute to the pathogenesis of pneumonia and how the host’s response to infection can be harmful as well as protective. The role of cytokines in pneumococcal pneumonia, the detailed behaviour of neutrophils in the disease, and the mechanisms by which the pneumococcus attaches to the host both during nasopharyngeal colonisation and during invasive disease have all been the subject of recent investigation. Whilst antibiotics and supportive care are likely to remain the keystone of the …