Microbiology

Streptococcus pneumoniae is a lancet-shaped, Gram-positive, facultative anaerobic organism. It is typically observed in pairs (diplococci), but can also occur alone or in short chains. Some pneumococci are encapsulated, their surface is composed of complex polysaccharides. The encapsulated organisms are pathogenic for humans and animals, and organisms without capsular polysaccharide are not. Capsular polysaccharide form the primary basis for pathogenicity of the organism. They are the antigen and form the basis for classifying pneumococci into serotypes. Ninety serotypes have been identified based on their reaction with type specific antisera. Type-specific antibodies against the capsular polysaccharide are protective against invasive infections. Interactions between these antibodies and complement factors ensure opsonisatie of pneumococci, which phagocytosis and clearance of the organism facilitated. Antibodies against some of the capsular polysaccharide may cross-react with related serotypes, like other bacteria. This can lead to protection against a broader group than those in the pneumococcal vaccine are present.

Most serotypes of S. pneumoniae causing a serious disease, but only a few serotypes are responsible for the majority of pneumococcal infections. It is estimated that the ten most common serotypes worldwide approximately 62% of all invasive infections by pneumococcus. Prevalence and classification of the serotypes responsible vary by age and geographic region. In Belgium taking in children under five years of the seven most common serotypes isolated approximately 80% of the infections in the blood and cerebrospinal fluid on their behalf.

Pneumococci are plentiful for in the airway and may give 5% to 70% of healthy adults are isolated from the nasopharynx. The incidence of asymptomatic carriage vary with age, environment and the presence of upper respiratory infections. Only 5% to 10% of adults without children are carriers. In schools and orphanages to 27% to 58% of the students and people carriers. In barracks could be 50% to 60% of the soldiers are carriers. The duration of the carrier varies and is generally longer in children than in adults. Moreover, the ratio of carrier to the development of natural immunity is still unclear

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