Clinical aspects and importance of pneumococcal infections.

Annualy in the USA, the estimated occurence of pneumococcal disease exceeds 500 000 cases of pneumonia (50 000 deaths), 1 200 000 cases of otitis media and 5 000 cases of meningitis. The pneumococcus remains the single most important pathogen which can cause pneumonia. When bacteremia accompanied pneumococcal pneumonia (one-fifth of these), the case fatality rate is approximately of 25% and exceeds 50% in individuals over 50 years of age. Most of the deaths (60%) occur within the first five days of illnesses, despite prompt antibiotic treatment of these patients. Emergence of pneumococcal strains with diminished sensitivity for penicillin, or resistant to tetracycline and other antibiotics is also a factor which lend increasing support to the concept that high risk patients should be protected from pneumococcal infection by immunoprophylaxis. A change of capsular types associated with bacteriemic disease has occured, in the USA, during the past three decades. The types 1 and 3 are less common than in the pre-antibiotic era, and the types 4, 8, 12, and 14 have become more prevalent. Infections with type 2, an epidemic type, have occured infrequently in the past 20 years. In the USA, at the present time, nearly four-fifths of bacteremic cases are associated with only 14 of the 84 pneumococcal capsular type ; in descending frequency : 8, 4, 1, 14, 3, 51, 12, 6, 56, 9, 19, 23, 5 and 20 (American system of nomenclature). The predominant capsular types of otitis media are : 1, 3, 6, 7, 14, 18 and 23. The polyvalent pneumococcal polysaccharide vaccine newly developed in the USA, is safe, antigenic and effective. Its widespread use can be expected to reduce the number of deaths attribuable to pneumococcal bacteremia.