Bacteria

Morphology

Cytology: Gram-positive, encapsulated, lancet-shaped diplococci; rarely short chains; intra- and extracellular; neutrophil-rich inflammation.

Histology: Acute neutrophil-rich, partly fibrinous inflammation; in pneumonia, intra-alveolar exudate composed of neutrophils, fibrin, and proteinaceous material.

Clinical notes

A common cause of pneumonia, otitis media and sinusitis. Invasive infections may lead to meningitis, bacteremia, and sepsis. Young children, older adults, and individuals with immunodeficiency or chronic underlying conditions are particularly at risk.

Ancillary Testing

Additional Information

Asymptomatic colonisation of the nasopharynx is common, particularly in children.

The polysaccharide capsule is the main virulence factor, inhibits phagocytosis and determines the serotype. More than 100 capsular serotypes are known (1).

Pneumococcal vaccines protect only against the serotypes they contain. Conjugate vaccines and a polysaccharide vaccine are available; recommendations depend on age and individual risk factors. Vaccination does not provide complete protection against all pneumococcal infections.