infectious diseases
Pneumococcal Infections
Serotypes
The pneumococcus capsule consists of a complex polysaccharide that determines serologic type and contributes to virulence and pathogenicity. Virulence varies somewhat within serologic types because of genetic diversity. 90 different pneumococcal serotypes have been identified based on their reaction with type-specific antisera. The pneumococcal polysaccharide capsule is critical for evading phagocytosis. Serotype 3 strains, which are more heavily encapsulated and tend to form more mucoid colonies than other serotypes, are common causes of invasive pneumococcal disease in adults. Most serious infections are caused by serotypes 3, 4, 6B, 9V, 14, 18C, 19F, and 23F, which are included in the most often initially given PCV15 and PCV20 Pneumococcal Vaccine . These serotypes cause about 90% of invasive infections in children and 60% in adults. However, these patterns are slowly changing, in part because of the widespread use of polyvalent vaccine. Serotype 19A, which is highly virulent and multidrug-resistant, has emerged as an important cause of respiratory tract infection and invasive disease; it is now included in the 15- and 20-valent pneumococcal conjugate vaccines. Additional infection-causing serotypes have been included in the updated 15- and 20-valent pneumococcal conjugate vaccines. 