Changing Epidemiology of Invasive Pneumococcal Disease among White Mountain Apache Persons in the Era of the Pneumococcal Conjugate Vaccine

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Abstract
Background. Prior to the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7), the rate of invasive pneumococcal disease (IPD) was 8-fold higher among White Mountain Apache persons of all ages than it was among the general US population. We aimed to assess the impact of PCV7 and 23-valent pneumococcal polysaccharide vaccine on the rate of IPD among White Mountain Apache persons. Methods. From 1991 through 2006, we conducted active laboratory- and population-based surveillance among Native American residents of the White Mountain Apache reservation. Charts were reviewed and pneumococcal isolates were collected for serotype testing. Three time periods were defined: the pre-PCV7 baseline period (1991–1997), the PCV7 efficacy trial period (1998–2000), and the PCV7 routine-use period (2001–2006). Results. We identified 246 cases of IPD; the mean annual IPD rate fell from 126 cases per 100,000 person-years in the period 1991–1997 to 87 cases per 100,000 person-years in the period 2001–2006 (P=.01). The rate of IPD attributable to PCV7 serotypes of Streptococcus pneumoniae decreased by 252 cases per 100,000 person-years (92%) among children aged ⩾5 years, and that attributable to non-PCV7 serotypes of S. pneumoniae decreased by 87 cases per 100,000 person-years (44%) among children aged ⩾5 years. Among adults, the rate of IPD remained unchanged; PCV7 serotypes of S. pneumoniae accounted for only 25% of adult cases during the period 1991–1997. Conclusions. Since the introduction of PCV7, the rate of IPD among White Mountain Apache children aged ⩾5 years has decreased to the lowest rate ever (122 cases per 100,000 person-years), but it remains 5.7-fold greater than the rate of IPD among children in the general US population. In contrast to some other high-risk populations, there is no evidence of non–vaccine-type replacement disease in this age group. Among White Mountain Apache adults, the rate of IPD remains substantially higher than that observed in the general US population. Vaccines with broader serotype coverage are needed to further reduce the disparity in the rate of IPD between the White Mountain Apache and general US populations.

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