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.