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Home Topics Infectious Diseases Infections A-Z Pneumococcal Disease General Information ›  Background Information on Pneumococcal Disease

Background Information on Pneumococcal Disease

Pneumococcal disease is the term used to describe infections caused by the bacterium Streptococcus pneumoniae (also called the pneumococcus). Following the successful introduction of Hib and meningococcal C conjugate vaccines, pneumococcal infection is now one of the most common causes of invasive bacterial infection in children.The pneumococcus is one of the most frequently reported causes of bacteraemia and meningitis. Invasive pneumococcal disease (IPD) is a major cause of morbidity and mortality, particularly affecting the very young, the elderly, asplenic (individuals without a spleen) and immunocompromised patients.

The organism

S. pneumoniae is an encapsulated Gram positive bacterium that usually gains entry into the human host by colonising the nasopharyngeal mucosal epithelium. Over 90 different pneumococcal serotypes have been identified based on the different complex sugar molecules (polysaccharides) that form their outer coating. The outcome of colonisation depends on the virulence of the specific serotype and on the host immune system. The capsule is the most important virulence factor of S. pneumoniae; pneumococci that lack the capsule are normally not virulent. About 66% of the serious infections in adults and about 80% of invasive infections in children are caused by eight to ten capsular types. Some serotypes of the pneumococcus may be carried at the back of the throat (nasopharynx) without symptoms, with disease occurring only in a small proportion of infected individuals. Other serotypes are rarely identified in the nasopharynx but are associated with invasive disease.

Clinical presentation

The organism may spread locally into the sinuses or middle ear cavity, causing sinusitis or otitis media (middle ear infection), particularly in children. It may also affect the lungs to cause pneumonia, or cause systemic (invasive) infections including bacteraemic pneumonia, bacteraemia and meningitis. The pneumococcus is also the commonest cause of community-acquired pneumonia (CAP). In children the pneumococcus is the most common bacterial cause of otitis media1.

1 Melegaro A et al. The current burden of pneumococcal disease in England and Wales. Journal of Infection 2006; 52: 37-48


Approximately 5,000-6,000 cases of invasive pneumococcal disease (isolates from blood, CSF or other normally sterile sites) are reported annually to Public Health England (PHE) from laboratories in England and Wales.


There is a marked seasonal pattern in the presentation of IPD with the greatest number of reports occurring between December and January.


Vaccination is currently recommended for all individuals aged over 65 years and from September 2006 for all children as part of the routine childhood immunisation programme, and also for all individuals in a high risk group for infection

There are two types of pneumococcal vaccine; polysaccharide (23vPPV) and conjugate vaccines (13V PCV). Since 1992, pneumococcal immunisation has been recommended for people with medical conditions for whom pneumococcal infection was likely to be more common or serious. For further details, please see vaccination section.

For more information please see, the revised Pneumococcal chapter of the Department of Health publication Immunisation Against Infectious disease [exterrnal link]    

This material is jointly produced by the Respiratory and Vaccine Preventable Bacteria Reference Unit and the Immunisation Department of Public Health England, Colindale.

For further information please also see Related Websites

Last reviewed: 23 October 2013