Pneumococcal disease:
a major health threat

• Streptococcus pneumoniae is a bacterium that causes a number of diseases.

• When the bacteria gain access to the blood or to other normally sterile sites they cause invasive disease. Invasive pneumococcal disease is serious and has a high risk of mortality.

• Pneumococcal disease is widespread, and despite the introduction of antimicrobial drugs over the past few decades it remains a significant threat to health.

• Otitis media (inflammation of the middle ear) caused by S. pneumoniae is a common disease in young children, but vaccination has limited effectiveness in preventing otitis media.

• Bacteraemia and meningitis are the most common invasive diseases.

• Pneumonia, bacteraemia and meningitis will be covered in detail.

• S. Pneumoniae is exclusively a human pathogen.

• The bacterium are often resident in the nasopharynx of persons who show no symptoms of infection.

• Colonisation of the nasopharynx can arise from inhalation of pneumococci transmitted by an asymptomatic carrier or a person with pneumococcal disease. Disease results from spread of the bacterium from the nasopharynx to other sites.

• Disease is usually caused by the spread from the site of colonisation.

• Pneumococcal proliferation in the middle ear causes otitis media; proliferation in the alveoli of the lungs causes pneumococcal pneumonia. (Both are non-invasive pneumococcal diseases.)

• Bacteraemia (invasive pneumococcal disease) occurs when pneumococci gain entry to the blood. Meningitis is caused by pneumococcal invasion of the cerebrospinal fluid (CSF).