Many serotypes of the bacterium Streptococcus pneumoniae.
Infection is acquired mainly through pneumococci contained in respiratory droplets. There are many healthy, asymptomatic carriers of the bacteria, but no animal reservoir or insect vector.
Nature of the disease
Pneumonia with empyema and/or bacteraemia, febrile bacteraemia and meningitis are the commonest manifestations of invasive pneumococcal infection. Pneumococci are a frequent cause of nonbacteraemic pneumonia. In developing countries, non-bacteraemic pneumonia causes the majority of pneumococcal deaths in children. Middle-ear infections, sinusitis and bronchitis are non-invasive and less severe manifestations of pneumococcal infection, but are considerably more common. Several chronic conditions predispose to serious pneumococcal disease. Increasing pneumococcal resistance to antibiotics underlines the importance of vaccination.
Pneumococcal infection is a major cause of morbidity and mortality worldwide. In 2005, WHO estimated that 1.6 million deaths were caused by this agent annually; this estimate included the deaths of 0.7–1 million children aged under 5 years. Most of these deaths occurred in poor countries and included a disproportionate number of children under the age of 2 years. In Europe and the USA, S. pneumoniae is the most common cause of community-acquired bacterial pneumonia in adults. In these regions, the annual incidence of invasive pneumococcal disease ranges from 10 to 100 cases per 100 000 population.
Risk for travellers
While travel itself does not normally increase the risk of acquiring pneumococcal disease, access to optimal health care may be limited during travel, increasing the risk of a poor outcome should disease occur. Thus, before undertaking travel to countries with limited medical resources, vaccination against invasive pneumococcal disease is advisable for children <2 years of age and for children and adults considered to be at particular risk of serious disease. Conditions predisposing to complications of pneumococcal infections include sickle-cell disease and other haemoglobinopathies, chronic renal failure, chronic liver disease, immunosuppression after organ transplantation, asplenia and dysfunctional spleen, leaks of cerebrospinal fluid, diabetes mellitus and HIV infection. Elderly individuals, especially those over 65 years of age, are also at increased risk for pneumococcal disease.