Streptococcus pneumoniae bacteraemia in Belgium:: differential characteristics in children and the elderly population and implications for vaccine use

The characteristics of bacteraemia with Streptococcus pneumoniae in children (0-4 years) and the elderly (greater than or equal to60 years) were compared over a 7 year period (1994-2000). Of a total of 7927 isolates of invasive S. pneumoniae studied in the national reference laboratory, 74% (n = 5837) were blood isolates. Of these 5837 S. pneumoniae bacteraemias, 843 (14%) occurred in children and 3144 (54%) in the elderly. The prevalence of penicillin resistance (MIC greater than or equal to 0.1 mg/L) in bacteraemic isolates rose from 8.2% to 18.9% (P = 0.03) in children and from 5.1% to 16.35% (P = 0.001) in the elderly over the study period. The prevalence of erythromycin resistance (MIC greater than or equal to 1 mg/L) in bacteraemic isolates was significantly higher in children than in the elderly (44.7% versus 25.7%, P = 0.001) and rose significantly over the 7 year period in the elderly (18.6-33.65%, P = 0.001). There were more serogroups and serotypes (SGTs) among the bacteraemic isolates obtained from the elderly compared with children (36 versus 26, P = 0.03). SGTs 6, 14, 18 and 19 cause significantly more bacteraemia in children than in the elderly. The opposite is true for SGTs 3, 7, 8, 9, 11, 12, 15, 20, 22 and 35. The new 7, 9 and 11 valent conjugate vaccine formulations cover significantly more bacteraemic SGTs in children than in the elderly (82%, 89.5% and 92% versus 55.5%, 65% and 77.5%, respectively; P = 0.001). The 23 valent polysaccharide vaccine provides a theoretical coverage of 95% in the elderly population. Our data indicate consideration of a vaccination strategy in the elderly population that combines the efficacy of conjugate vaccines with the broad coverage of the 23 valent polysaccharide vaccine.