Changing epidemiology of invasive pneumococcal disease among White Mountain Apache persons in the era of the pneumococcal conjugate vaccine.

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.

Invasive pneumococcal disease among White Mountain Apache adults, 1991-2005.

BACKGROUND: Certain Native American populations have high rates of invasive pneumococcal disease (IPD). We aimed to determine the disease spectrum and risk factors of White Mountain Apache adults (age, >or=18 years) with IPD and the use and effectiveness of pneumococcal polysaccharide vaccine (PPV) in this population. METHODS: We conducted active surveillance for IPD between 1991 and 2005. Medical records were reviewed, and isolates were serotyped. Vaccine use was assessed in 2004-2005 among White Mountain Apache adults with an indication for pneumococcal vaccination. The effectiveness of PPV was determined through an indirect cohort method. RESULTS: Among the 115 IPD cases (in 109 persons), the mean age was 43 years; 62% were male; 91% had risk factors, and alcoholism predominated (73%). Alcoholic patients were younger (mean age, 40.1 years; P<.001) and more often male (70%; P=.001) compared with nonalcoholic patients. The case fatality rate was 15%; all deaths occurred among those with risk factors. Only age 65 years or older was associated with increased risk of death. Of 447 White Mountain Apache persons at high risk, 76% had received PPV. Vaccination rates were highest among subjects with pulmonary disease (95%) and diabetes (89%) and lowest among those aged 50 to 64 years (40%). Of the 115 IPD cases for which serotypes were available, 77% were due to serotypes contained in PPV. The effectiveness of PPV against serotype-specific IPD, as measured by the indirect cohort analysis of IPD cases, was 68% (95% confidence interval, 3%-90%). CONCLUSIONS: Among White Mountain Apache adults with IPD, alcoholism is common and contributes to the younger age and male predominance of cases. Pneumococcal vaccination rates are high, and there is suggestive evidence of the effectiveness of PPV in this population. Additional preventive strategies, including risk factor modification and vaccination of younger high-risk adults, should be pursued.