Emergence and spread of azithromycin-resistant Neisseria gonorrhoeae in Scotland

OBJECTIVES: The aim of this study was to analyse the trend in azithromycin susceptibility (AzDS) of Neisseria gonorrhoeae in Scotland between April 2004 and December 2007, and to characterize isolates exhibiting decreased AzDS or high-level azithromycin resistance (AzHLR). METHODS: Antibiotic susceptibility testing and N. gonorrhoeae multiantigen sequence typing (NG-MAST) were performed on all gonococcal isolates received by the Scottish Bacterial Sexually Transmitted Infections Reference Laboratory (SBSTIRL) during the study period. RESULTS: AzHLR isolates were observed for the first time in 2004 and increased from 0.3% to 3.9% in 2007. AzDS declined from 2.1% to 1.3% in the same period. Taken together, AzDS and AzHLR isolates accounted for 5.2% of the gonococcal infections in Scotland in 2007. NG-MAST revealed that only a small number of sequence types (STs) contained AzHLR and AzDS isolates; these STs also included azithromycin-susceptible isolates. Most STs containing AzHLR isolates were genetically related on the basis of their por and tbpB alleles; however, demographic data suggested that they formed discrete sexual networks. CONCLUSIONS: AzHLR strains of N. gonorrhoeae are increasing in Scotland. A 1 g dose of azithromycin should not be considered as an alternative antibiotic therapy for gonococcal infections. The use of azithromycin to treat chlamydia in patients co-infected with N. gonorrhoeae results in a level of azithromycin in vivo that is sublethal for N. gonorrhoeae, which may lead to resistance.