Serogroups/types and antibiotic resistance of referred isolates of Streptococcus pneumoniae: 1993 to 1995.

Surveillance of prevalent serogroups/types of Streptococcus pneumoniae and their susceptibility to antimicrobial agents is important for understanding the epidemiology of pneumococcal infections and for guiding empirical treatment. Current vaccines for prevention of pneumococcal infection utilise serotype specific antigens, so knowledge of the prevalence of particular serotypes is relevant to vaccine use and development. Five thousand seven hundred and ninety-six isolates of S. pneumoniae from separate patients were serogrouped or serotyped by the Streptococcus and Diphtheria Reference Unit between 1993 and 1995. Antibiotic susceptibility testing was carried out by the Antibiotic Reference Unit on 3821 (65.9%) of these isolates. A total of 40 distinct serogroups/types, together with a small number of non-typable isolates, were noted over the three year period. The same five serogroups/types (6, 9, 14, 19, and 23) occurred most commonly in each year of the study, not only in the total population of isolates studied, but also in isolates obtained from blood or cerebrospinal fluid, and among isolates with antibiotic resistance. Ninety-six per cent of the isolates belonged to serogroups/types included in the currently available 23-valent capsular polysaccharide pneumococcal vaccine; the conjugate petna-, hepta-, and nonavalent vaccines covered 51%, 75%, and 80% of isolates respectively. The nonavalent vaccine offers the most promise as 74% of all blood and cerebrospinal fluid isolates and 90% of antibiotic resistant isolates belonged to serogroups or types included in this formulation.