Recent trends in the epidemiology of gonorrhoea in Sweden : the role of importation and core groups

Abstract

In 1997 the gonorrhoea incidence in Sweden started to rise from a low-prevalent level after some 25 years of steady decline. The rise has continued and coincides with similar trends in other sexual transmitted infections (STIs) and in other Western industrialized countries.

Gonorrhoea is included in the Swedish Communicable Diseases Act and all diagnosed cases should be reported. Additional epidemiological data were collected during 12 months in 1998-99 about all reported cases (n=357), which then were linked to microbiological characterization of the isolated Neisseria gonorrhoeae (Ng) strains. Analyses showed that the increase of gonorrhoea is mainly due to an increase of domestic cases: 60% were acquired in Sweden, especially in Stockholm. Heterosexual teenagers and men who have sex with men (MSM) were identified as endemic core groups infected by separate phenotypic Ng serovars. In total, 28 different serovars were identified. Among imported cases, Thailand was the most prevalent country of exposure.

Further genotypic characterization by PFGE indicated that one Ng clone each of the serovars IB-2 and IB-3 created the majority of the two identified core groups of domestic cases in Sweden 1998-99. When analysing isolates other than those belonging to the two genetically indistinguishable clones, PFGE identified a high genetic diversity within and between the different serovars.

The antibiotic susceptibility varied with the countries where the patients were exposed. When exposed in Asia, 63% of the isolates showed reduced susceptibility to ciprofloxacin (MIC>0.064 mg/l), compared with 0%-8.5% of the isolates from patients exposed in other countries (RR=8.5, p<0.001). Ciprofloxacin cannot be recommended as first choice of treatment if the patient was exposed in Asia. All strains were fully susceptible to spectinomycin and ceftriaxone, which are better choices of treatment.

In a long-term study of gonorrhoea among MSM in Stockholm (n=840 cases), a great variation of different serovars (n=66) was seen during a 15-year period, indicating a continuous importation of strains into this core group and possible micro-epidemics caused by only a few persistent serovars. A significant difference (p=0.001) was observed in the distribution of serovars correlated to HIV status. The prevalence of HIV among all cases was 10%. Thus, gonorrhoea is a marker for HIV infection in MSM, but the increase in gonorrhoea may be associated with genital-oral sexual practice rather than with high risk sexual practice. Also, a sexual behaviour study in MSM, showed an increase in the reported number of sexual partners (p<0.001) and in unprotected oral sex with casual partners (p<0.05), findings that are associated in time with the increase of gonorrhoea among MSM.

Further active surveillance of gonorrhoea, including epidemiological data and microbiological characterization, is needed to control the spread and to make it possible to direct intervention efforts to core groups and persons at risk.