Temporal changes in the gonococcal serovar patterns in Stockholm during two years with special reference to PPNG strains.

OBJECTIVE

To analyse temporal changes in gonococcal serovar patterns in Stockholm during a two year study period (1987-1989) to elucidate the dynamics of gonorrhoea epidemiology.

DESIGN

The study population comprised 857 patients with culture proven gonorrhoea and with serotyped gonococcal isolates. The probable geographical origin of the infection was determined in 690 of the patients.

RESULTS

A total of 108 Ph/GS-serovars were identified. Most (73%) of the serovars were recognised only during one or two quarters of the study period and comprised 16% of the isolates. Seven serovars were encountered during all eight quarters. Three of these serovars i.e. Arost/Aedgkih (IA-1, IA-2), Bropt/Bajk (IB-3, IB-6), Brpyust/Bacejk (IB-1, IB-2) were the most prevalent in the overall study, accounting for 60% of the isolates during the first quarter of the study and 36% of the isolates during the last quarter. Fifty-seven percent of the patients were infected in Stockholm (endemic infection). The proportion of endemic isolates among the three most common serovars declined throughout the study period (77% during the first quarter; 47% during the last quarter). A total of 32 Ph/GS-serovars were recognised among 80 PPNG strains. Only four of these 32 serovars were encountered during more than two quarters. Of 57 patients with PPNG strains and with geographical origin of the infection known, only seven (12%), all infected in Sweden, might have transmitted their infection further into the society.

CONCLUSIONS

The decline in the total number of gonorrhoea cases seen in Stockholm during the study period, was due mainly to a decline of endemic isolates of the three most prevalent serovars. Results from contact tracing and serotyping indicated that PPNG infections acquired abroad seldom become established in the community. Serovar determination seems valuable mainly as a tool for surveillance whereby the introduction and circulation of gonococcal strains in the community can be pursued.