prevention at the present time. Thus, in this chapter, the committee has chosen to highlight pneumococcal infections, influenza, and nosocomial infections. Each deserves high priority for prevention because each is a serious risk factor for the elderly and can be prevented to a great extent with existing interventions.

PNEUMOCOCCAL DISEASE

Pneumococcal disease has long been recognized as an important risk factor for the elderly. This category includes pneumonia, bronchitis, bacteremia, and meningitis caused by any one of the 83 serotypes of Streptococcus pneumoniae. Pneumococcal pneumonia is the most common form of community-acquired pneumonia in the elderly, accounting for up to 60 percent of cases14,34,35,36,37,52 and for up to 20 percent of nosocomial pneumonias.10,52 Pneumococcal bacteremia, which is more easily proven than pneumococcal pneumonia, occurs in up to one-quarter of cases of pneumococcal pneumonia. Population-based studies have shown that the elderly sustain the highest pneumococcal bacteremia rates of any population group—50 per 100,000 persons over the age of 65,36,37 which is more than three times greater than the rates for younger persons.

The costs of pneumococcal diseases are great because the elderly require hospitalization and the illnesses often cause complications.26,32 Although pneumococcal pneumonia does not result in permanent lung damage, complications from bacteremia and meningitis are common and can damage other organ systems. Death rates from pneumococcal bacteremia range from 20 to 80 percent, increasing with age and complications.10,26,36,37

Although antibiotics are considered to be effective in the treatment of pneumococcal diseases, deaths and complications often occur despite the prompt use of effective antibiotics. Further reductions in morbidity and mortality from pneumococcal diseases require that preventive measures be used. Pneumococcal polysaccharide vaccine is the only currently available preventive measure. This vaccine was first developed in the 1940s but was temporarily abandoned with the advent of antibiotics. With growing recognition of the limitations of antibiotics, the vaccine was again introduced in the late 1970s. Some of the controlled studies of the vaccine have not demonstrated a protective effect;16,48 other research, including case-control studies, have shown pneumococcal vaccine to be both immunogenic43,44 and safe,15 and to provide up to 70 percent efficacy in the elderly.50,51 A vaccine works by providing protective levels of type-specific antibodies. Confidence in the effectiveness of the current 23-valent pneumococcal



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