Epidemiology of invasive Streptococcus pneumoniae infections in the United States, 1995-1998: Opportunities for prevention in the conjugate vaccine era

Abstract

Context: Pneumococcal polysaccharide vaccine is recommended for elderly persons and adults with certain chronic illnesses. Additionally, a recently licensed pneumococcal 7-valent conjugate vaccine has been recommended for use in young children and could dramatically change the epidemiology of pneumococcal disease.

Objectives: To assess pneumococcal disease burden in the United States, estimate the potential impact of new vaccines, and identify gaps in vaccine recommendations.

Design and setting: Analysis of data from the Active Bacterial Core Surveillance (ABCs)/Emerging Infections Program Network, an active, population-based system in 9 states.

Patients: A total of 15 860 cases of invasive pneumococcal disease occurring between January 1, 1995, and December 31, 1998.

Main outcome measures: Age- and race-specific pneumoccocal disease incidence rates per 100 000 persons, case-fatality rates, and vaccine preventability.

Results: In 1998, overall incidence was 23.2 cases per 100 000, corresponding to an estimated 62 840 cases in the United States. Incidence was highest among children younger than 2 years (166.9) and adults aged 65 years or older (59.7). Incidence among blacks was 2.6 times higher than among whites (95% confidence interval [CI], 2.4-2.8). Overall, 28.6% of case-patients were at least 65 years old and 85.9% of cases in this age group were due to serotypes included in the 23-valent polysaccharide vaccine; 19.3% of case-patients were younger than 2 years and 82.2% of cases in this age group were due to serotypes included in the 7-valent conjugate vaccine. Among patients aged 2 to 64 years, 50.6% had a vaccine indication as defined by the Advisory Committee on Immunization Practices (ACIP). The case-fatality rate among patients aged 18 to 64 years with an ACIP indication was 12.1% compared with 5.4% for those without an indication (relative risk, 2.2; 95% CI, 1.7-2.9).

Conclusions: Young children, elderly persons, and black persons of all ages are disproportionately affected by invasive pneumococcal disease. Current ACIP recommendations do not address a subset of persons aged 18 to 64 years but do include those at highest risk for death from invasive pneumococcal disease.