Ninety serotypes of S. pneumoniae have been identified with varying degrees of pathogenicity, out of which 23 serotypes are known to cause disease in humans. S. pneumoniae serotypes 3, 4, 6B, 9V, 14, 18C, 19F, and 23F cause the majority of invasive disease. S. pneumoniae causes (a) pneumonia, (b) meningitis, (c) sinusitis and otitis media, (d ) bacteremia, and (e) other infections.
S. pneumoniae is the leading cause of bacterial pneumonia, bothlobar and bronchopneumonia. Pneumonia develops when bac-terium multiplies in the alveoli. Since the disease is associated with aspiration and is localized in the lower lobes of the lungs, it is called lobar pneumonia. Pneumonia is common at the extreme of ages, in children and in elderly, who have a more generalized bronchopneumonia.
S. pneumoniae is the most common bacterial cause of child-hood pneumonia, especially in children younger than 5 years. Serotypes 6, 14, 18, 19, and 23 are responsible for most cases of pneumonia in children, while serotypes 1, 3, 4, 7, 8, and 12 cause pneumonia in adults leading to mortality in more than 5–10%.
Haemophilus influenzae and Moraxella catarrhalis are the othercauses of acute pneumonia. Mycoplasma pneumoniae,Chlamydiapneumoniae and Legionella spp. are the causative agents of atypi-cal pneumonia.
Pneumococcus is the most common cause of pyogenic men-ingitis in children, although the condition can occur in all age groups. Meningitis is always secondary to other pneumococ-cal infections, such as pneumonia, bacteremia, infections of the ear or sinuses. The bacteria reach the brain through blood stream or from nasopharynx (following head trauma or dural tear particularly with cerebrospinal fluid leak).
Pneumococcal meningitis is now emerging as a com-mon cause of death in children and in adults. Meningitis caused by S. pneumoniae is associated with a higher mortal-ity and more neurological complications than the menin-gitis caused by any other bacteria. Even with antibacterial therapy, the mortality due to pneumococcal meningitis is nearly 25%.
Streptococcus agalactiae, Escherichia coli, Neisseria meningitidis, H. influenzae type B, Listeria monocytogenes, Pseudomonas spp.,Flavobacterium meningosepticum, and Staphylococcus aureus are theother bacteria causing meningitis.
Sinusitis and otitis media occur in patients with prior viral infections. The viral infection lowers the mucosal immunity, facilitating the invasion by S. pneumoniae. Sinusitis caused by the pneumococci occurs in patients of all ages, but otitis media caused by the bacteria is seen only in young children. Pneumococci cause approximately 40% of otitis media cases. H. influenzae is another causative agent.
This condition is more frequent in children than in adults. Bacteremia occurs in more than two-thirds of patients with meningitis and in one-fourth of the patients with pneumococ-cal pneumonia. This does not occur in patients with sinusitis or otitis media.
These include spontaneous bacterial peritonitis, postsplenec-tomy sepsis, endocarditis associated with rapid destruction of heart valves, bone and joint infections (prosthetic or natural joint septic arthritis, occasionally as a complication of rheu-matoid arthritis), myositis, and brain and epidural abscesses. All these infections result from seeding of tissues during bacteremia.