title: Rapid spread in Norway of an erythromycin-resistant pneumococcal clone, despite low usage of macrolides.
abstract: During the last 4 years, Norway has experienced an increase in macrolide resistance among systemic isolates of Streptococcus pneumoniae. The Norwegian reference laboratory for pneumococci received the isolates from over 85% of the Norwegian cases of systemic pneumococcal disease in the period studied. To study the details of the increased macrolide resistance, all macrolide-resistant systemic pneumococcal isolates (410 isolates) collected in the period from 1995 to 2005 were characterized phenotypically, and a representative selection of 68 strains was also studied genotypically. The serogroups most frequently associated with macrolide resistance in the studied period were 14, 6, 23, 19, and 9. The resistance M-type was expressed in 85% of the resistant isolates. Of the 68 isolates analyzed by multilocus sequence typing, 19 different sequence types (STs) were represented, including several of the international resistant clones. All but one of the clones appeared at a low frequency; mainly as isolated cases. The increase in macrolide resistance seen from 2001 to 2005 proved to be caused by ST-9, defined as the England(14)-9 clone by the Pneumococcal Molecular Epidemiology Network. All ST-9 isolates tested, carried the mef(A) gene and expressed the resistance M-type. This clone first appeared in the Oslo region in 1993, but was by 2005 isolated from all over the country. Children were overrepresented among the cases caused by this clone; however, people aged 20-29, possibly involving the parent generation, were also represented at an increased frequency. The England(14)-9 clone has been able to spread successfully in the Norwegian population despite a relatively low consumption of macrolides.
authors.affiliation: Division of Infectious Disease Control, Norwegian Institute of Public Health, Nydalen, NO-0403 Oslo, Norway.
authors.forename: Maren K R
authors.initials: MK
authors.lastname: Sogstad
authors.forename: Pia
authors.initials: P
authors.lastname: Littauer
authors.forename: Ingeborg S
authors.initials: IS
authors.lastname: Aaberge
authors.forename: Dominique A
authors.initials: DA
authors.lastname: Caugant
authors.forename: Arne
authors.initials: A
authors.lastname: Høiby
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques; D002648:Child; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology*; D005838:Genotype; D006801:Humans; D018942:Macrolides / Q000494:pharmacology; D009664:Norway / Q000453:epidemiology; D010641:Phenotype; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000235:genetics / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D004917:Erythromycin