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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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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 ...