Aims
To phenotypically and genotypically characterise clinical N. gonorrhoeae isolates transmitted in Sweden during 2005 and to compare with characteristics of N. gonorrhoeae populations in other countries.
Introduction
In Sweden, the gonorrhoea incidence decreased from the beginning of the 1970s to 1996. From 1997 the incidence has almost annually increased, mainly due to a rise in domestic cases of young heterosexuals of both sexes and homosexual men. Furthermore, during recent decades resistance to most of the traditional antibiotics used in the treatment of gonorrhoea has rapidly increased worldwide. Availability of effective diagnostics, treatment and surveillance of epidemiological characteristics (antibiotic susceptibility, serovars and genotypes) are main tools for control of the transmission of infection.
Materials, Methods & Results
N. gonorrhoeae isolates (n=175) cultured in Sweden in 2005 and received at the Swedish Reference Laboratory for Pathogenic Neisseria were included. Phenotypic characterisation was performed by antibiotic susceptibility testing and serovar determination using both Genetic systems (GS) and Pharmacia (Ph) panels of monoclonal antibodies (MAbs). Genetic characterisation was performed using N. gonorrhoeae multiantigen sequence typing (NG-MAST) that analyses more variable segments of the porB gene (490 bp) and of the tbpB gene (390 bp).
All isolates were susceptible to cefixime, ceftriaxone, and spectinomycin. The levels of intermediate susceptibility and resistance to azithromycin, ciprofloxacin, and ampicillin were 2.3%, 49.7% and 75.3%, respectively (Table 1). Fifty-seven (33%) of the isolates were -lactamase producing.
In total, 33 of the isolates were determined as serogroup WI (PorB1a). These were assigned nine different GS-serovars and seven different Ph-serovars. Two of the PorB1a isolates were not serotypeable using Ph MAbs. The remaining 142 isolates were determined as serogroup WII/III (PorB1b). These isolates were assigned 18 different GS-serovars and 38 different Ph-serovars.
The isolates displayed 66 and 56 divergent NG-MAST porB and tbpB alleles, respectively. These resulted in assignment of 95 different sequence types (STs), of which 34 have not been previously described. ST40 (n=15), ST225 (n=12), ST1813 (n=9), ST5 (n=8), ST753 (n=6), ST323 (n=5), and ST211 (n=4), were the most prevalent STs. Four STs were represented by three isolates, 20 STs by two isolates and 64 STs by single isolates (Figure 1).
Conclusions
A highly diverse N. gonorrhoeae population was transmitted in Sweden during 2005, which can reflect importation of strains from abroad, and/or in some geographic areas suboptimal diagnostics and incomplete epidemiological surveillance. However, many clusters of isolates, which can reflect the existence of several transmission chains, were also identified.
Serovar determination is still fairly effective, rapid, inexpensive, easily performed and remains a valuable primary epidemiological marker of N. gonorrhoeae, which can supplement the superior genetic characterisation.