Nasopharyngeal carriage of Streptococcus pneumoniae in Navajo and White Mountain Apache children before the introduction of pneumococcal conjugate vaccine.

BACKGROUND: Infants and children are frequently colonized with pneumococcus. Recent nasopharyngeal acquisition of pneumococcus is thought to precede disease episodes. The increased risk of pneumococcal disease among Navajo and White Mountain Apache populations has been documented. Little is known about the dynamics of pneumococcal carriage in these populations. METHODS: A group randomized, controlled trial of 7-valent conjugate pneumococcal vaccine (PnCRM7, Wyeth) was conducted on the Navajo and Apache reservations. A nasopharyngeal (NP) carriage study was nested in the trial to evaluate the impact of PnCRM7 on carriage. Children <6 years of age had NP swabs collected at enrollment and at 6 and 12 months following enrollment. We analyzed carriage data from children in control vaccine randomized communities to describe the epidemiology of pneumococcal carriage. RESULTS: Of the 410 participants enrolled, 92% were colonized with pneumococcus at least once during the course of the study. Sixty-three percent of NP specimens were positive for pneumococcus. The most common serotypes were 6A, 6B, nontypable, 23F, 14, 19F, 19A, and 9V. Thirty-eight percent of isolates were vaccine serotypes. Age <2 years, male sex, daycare attendance, and having a sibling colonized with pneumococcus were associated with an increased risk of carriage. CONCLUSIONS: The high carriage prevalence among Navajo and Apache children reflects an intense exposure to pneumococcus. The lack of modifiable risk factors for carriage highlights the importance of preventive strategies for disease control.