Infections Due to Streptococcus pneumoniae

Pneumococci, or Streptococcus pneumoniae, are gram-positive, lancet-shaped diplococci but may also grow in short chains. The polysaccharide polymer that forms the outer capsule of S pneumoniae is chemically and antigenically unique and is crucial to virulence. There are at least 90 distinct serotypes. The capsule allows the bacteria to resist phagocytosis by leukocytes unless the organisms have been opsonized by antibody or serum complement components. Certain pneumococcal serotypes, such as the heavily encapsulated type 3 pneumococcus, are particularly virulent. In fact, only 23 serotypes account for 80% of bacteremic pneumococcal infections in the United States; capsular polysaccharides from these 23 serotypes are incorporated into the polyvalent polysaccharide pneumococcal vaccine (PPSV23), which has been available since 1983. This review covers the epidemiology and pathogenesis of pneumococcal infections, clinical pneumococcal infections, and prevention of pneumococcal infections. Adverse outcomes in pneumococcal pneumonia, antibiotic treatment for penicillin-resistant S pneumoniae, and Centers for Disease Control and Prevention child and adolescent immunization schedules are discussed. This review contains 1 figure, 6 tables, and 41 references.  Key words: bacterial pneumonia, PCV13, penicillin-resistant Streptococcus pneumoniae, pneumococcal pneumonia, pneumococcus, PPSV23, pneumonia vaccine, Streptococcus pneumoniae