Clinical and microbiological epidemiology of Streptococcus pneumoniae bacteraemia

A survey of Streptococcus pneumoniae bacteraemia in the Grampian region of Scotland was carried out over a 2-year period. One hundred and four bacteraemic episodes were identified in 103 patients, an incidence of 9.8/100,000 population/year, and the mortality was 24%. Clinical information was abstracted from 92 sets of patient notes and 98 isolates of S. pneumoniae were available for further study. The incidence of S. pneumoniae bacteraemia was highest at the extremes of age and peaked at 78 cases/100,000 population/year in those over 80 years old. Many patients had predisposing conditions, of which chronic lung disease (23%), chronic alcohol abuse (10%) and malignant disease (10%) were the commonest. Age was the highest risk factor for mortality, with 20 of the 22 deaths in those over 65 years old. The commonest serotype of S. pneumoniae isolated was serotype 14 (23.5%). Only one isolate (serotype 6A) showed intermediate resistance to penicillin, but 12 isolates (12.2%) were resistant to erythromycin. Nine of these 12 isolates were of serotype 14 and had MICs clustered in the range 12-24 mg/L. Examination of all serotype 14 isolates by pulsed-field gel electrophoresis (PFGE) showed the presence of two distinct genetic clusters, with all the erythromycin-resistant isolates in the same cluster. These isolates had similar PFGE profiles to erythromycin-resistant serotype 14 strains isolated elsewhere in the UK and they were positive for the mefE gene by PCR, confirming that resistance was of the M phenotype. The recent increase in erythromycin resistance in S. pneumoniae may be due, at least in part, to the spread of a serotype 14 clone of the M phenotype which appears to be an important cause of invasive disease.