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Causes of pneumococcal infection
Medical expert of the article
Last reviewed: 04.07.2025
Causes of pneumococcal infection
Pneumococcus (Streptococcus pneumonie) is a gram-positive diplococcus of oval or lanceolate shape, surrounded by a polysaccharide capsule. Belongs to the genus Streptococcus of the family Streptococcaceae. Depending on the structure of the capsular antigen, 85 serotypes have been identified. The main pathogenicity factors are: the capsule, which suppresses phagocytosis, and the teichoic acids of the cell wall, which react with CRP. Pneumococcus grows on nutrient media containing protein, is resistant in the environment, and is sensitive to the action of disinfectants. Pneumococcus is sensitive to antibacterial drugs of various groups.
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Pathogenesis of pneumococcal infection
Depends on the clinical form of pneumococcal infection. In the development of manifest forms of the disease, the virulence of the pathogen strain and a decrease in the resistance of the mucous membrane of the upper respiratory tract, nonspecific and specific protective factors are important. Due to the presence of a capsule, pneumococcus is protected from phagocytosis. Teichoic acids activate the complementary cascade and initiate the release of mediators of the acute phase of inflammation, which leads to tissue damage. From the upper respiratory tract, the pathogen penetrates the paranasal sinuses by contact, through the Eustachian tube - into the middle ear; by contact and lymphogenously from the middle ear, main, ethmoid and frontal sinuses it reaches the membranes and substance of the brain. Hematogenous spread of pneumococcus with the development of pneumonia, septicemia (pneumococcemia), endocarditis and primary meningitis is also possible.
Epidemiology of pneumococcal infection
The source of pneumococcal infection is healthy carriers and patients with pneumonia, as well as pneumococcal rhinitis. The main route of transmission is airborne droplets, contact is possible. Susceptibility is low. Pneumococcal infections are widespread (80% of community-acquired pneumonia, otitis, sinusitis, 30% of bacterial meningitis). When infected, a healthy carriage or rhinitis usually develops. The duration of a healthy carriage in children is 3-4 weeks, in adults - up to 2 weeks. The frequency of carriage is higher in children's groups, in winter it is higher than in summer. Serotypes 6, 14.19 and 23 are more often detected in children, in adults - serotypes 1, 3, 4, 7-9 and 12. As a result of carriage, type-specific immunity is formed. Its duration and intensity have not been established.