Nasopharyngeal carriage

The pneumococcus is one of the most common etiologies of respiratory tract infections like sinusitis, otitis media, and pneumonia, as well as nonrespiratory infections like meningitis, sepsis, and bacteremia. The authors presume the existence of special niches for pneumococcal attachment and the subsequent establishment of colonization, processes in which the newly arriving pneumococcus has to evade the local host defenses and compete with the resident polymicrobial flora, including other strains of pneumococci. Pneumococcal colonization induces a variety of immune responses in humans, including the production of antibodies directed at both surface proteins and the PS capsule. This chapter defines the direct effect of vaccine on carriage as those effects observed among the vaccinated individuals These effects include the impact on vaccine type (VT) carriage, vaccine-associated serotype carriage, nonvaccine type (NVT) carriage, and nonpneumococcal NP carriage. Haemophilus influenzae and Moraxella catarrhalis are common constituents of the microflora of the human nasopharynx and, after pneumococci, are the most common causes of upper respiratory infection; therefore, they could be expected to be affected by changes in pneumococcal colonization. The experience accumulated from the large-scale use of pneumococcal conjugate vaccine (PCV) has also allowed an analysis of the immunization schedule. The direct effect of PCV on pneumococcal carriage is to reduce vaccine serotype and increase nonvaccine serotype colonization among vaccinated children. There are three phases of a nasopharyngeal colonization episode: acquisition, the period of colonization, and clearance of the organism.