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Streptococcus pneumoniae, Staphylococcus aureus, and group A Streptococcus pyogenes are the three most important bacterial pathogens causing infections in otherwise well children. In 2005 it was estimated that S pneumoniae caused 700,000 to 1 million deaths in children younger than 5 years of age. Most of these children lived in developing countries.1

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There are 90 immunologically and chemically distinct capsular polysaccharides that determine virulence. Based on antigenic similarities, the 90 types have been grouped into 45 serotypes. Relatively few serotypes cause most disease, which has lead to development of polyvalent vaccines.2

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S pneumoniae can cause infection in almost any tissue or organ. The vast majority of infections in children occur in the middle ear, sinuses, lungs, meninges, and bloodstream. In 2000, the Food and Drug Administration approved and the Advisory Committee on Immunization Practices recommended the heptavalent pneumococcal conjugate vaccine (PCV7) for routine use in infants and young children as a primary series at 2, 4, and 6 months of age and a booster dose at 12 to 15 months of age.3 This vaccine has had an impressive effect on the incidence of invasive pneumococcal disease in vaccine recipients and the general population (see Chapter 244).

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Epidemiology

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Recent nasopharyngeal colonization with a new serotype almost always precedes infection.4,5 Colonization rates are highest in infants and preschool children, where they may be as high as 35%.4 Children may carry different serotypes at different times but are almost always colonized by those limited serotypes responsible for infections in this age group.2 Carriage rates are lower in older children (40–50%) and in adults (5–30%).6,7 PCV7 includes the 7 most common serotypes causing colonization and infection in children (4, 6B, 9V, 14, 18C, 19F, and 23F). These serotypes and the cross-reactive serotypes (6A, 9A, 9L, 18B, 18F) caused 86% of cases of bacteremia, 83% of cases of meningitis, and 65% of cases of acute otitis media in children younger than 6 years.3 These serotypes also accounted for more than 80% of penicillin-resistant colonizing serotypes.8

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PCV7 was licensed for use in the prevention of invasive pneumococcal disease (a positive culture from a normally sterile body site, eg, meningitis and bacteremia) in infants and toddlers. In the Northern California Kaiser Permanente Vaccine Study among 37,686 infants, vaccine efficacy was 97.4% compared with placebo for vaccine serotype invasive pneumococcal disease.9 In the same study population, episodes of pneumonia with an abnormal chest radiograph with consolidation or empyema were reduced by 17.7%. In a separate study population, vaccine efficacy for otitis media was demonstrated but to a more modest degree (6% for all cases of otitis media, 34% for culture-confirmed pneumococcal episodes, and 57% for otitis media caused by the pneumococcal serotypes contained in the vaccine).10

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Since the release of PCV, the rates of colonization and invasive pneumococcal disease ...

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