The burden of pneumococcal disease among adults in developed and developing countries: what is and is not known.

The burden of pneumococcal disease among adults in developed countries is neither widely known nor appreciated. The incidence of pneumococcal pneumonia is uncertain because a precise diagnosis cannot be obtained for most patients. Population-based data on invasive pneumococcal disease (e.g., bacteraemia and meningitis) suggest an annual incidence in all developed countries of > or =15-20 cases per 100,000 persons of all ages and > or =50 cases per 100,000 elderly adults (> or =65 years). In developing countries there are no population-based data on the burden of pneumococcal disease among adults. Studies of high risk groups, hospital-based studies, vaccine efficacy trials, extrapolations from surveillance of "native populations" in developed countries, and demographic studies in developing regions all suggest a high burden of disease. The broad variation in these estimates, however, indicates that better studies are needed. Increased use of pneumococcal vaccines among adults in all countries will depend on better scientific and public understanding of the burden of pneumococcal disease. In developing countries, intensive community-based studies of the impact of pneumococcal disease, or, alternatively, a "vaccine probe" approach, in which a population is vaccinated and the reduction in pneumonia is compared with that in a control population, could give more accurate estimates of the burden of disease and of the potential effectiveness of pneumococcal vaccination among adults.