The sac-4 gene of Neisseria gonorrhoeae and co-existing chlamydial infection

D J Phillips¹, C Patrizio¹, A Moyes¹ and H Young¹

¹ Scottish Neisseria gonorrhoeae Reference Laboratory, Department of Medical Microbiology, Edinburgh University Medical School, Teviot Place, Edinburgh EH8 9AG, UK

Correspondence to:
Dr Hugh Young Hugh.Young{at}ed.ac.uk

Background/objectives: Recently, the sac-4 gene in Neisseria gonorrhoeae was postulated to increase the risk of developing mixed gonococcal and chlamydial infection. The aims of this study were to determine the frequency of the sac-4 gene in a larger sample of isolates of different serovars and to assess the prevalence of sac-4 in gonococcal isolates from patients with and without coexisting chlamydial infection.

Methods: Isolates from 259 episodes of gonorrhoea were tested by a PCR assay for the sac-4 gene. The presence of co-existing chlamydial infection was determined from both laboratory and GUM clinical records.

Results: The overall prevalence of sac-4 was 57.5% (149/259). The prevalence was not the same in all serovars and ranged from 34.9% in serovar 1B2 to 100% in serovar 1B18. Exact logistic regression analysis indicated significant differences in sac-4 prevalence in isolates of different serovars. The prevalence of sac-4 was 69.5% (41/59) in gonococcal isolates from patients with co-existing chlamydial infection compared with 57.9% (62/107) for those without chlamydial infection. Exact logistic regression analysis showed that the slightly increased sac-4 prevalence among chlamydia positive patients (p=0.2) virtually disappeared when serovar status was taken into account (p>0.9).

Conclusion: The sac-4 gene of the gonococcus does not increase the risk for mixed chlamydial infection.

Key Words: dual infection; Neisseria gonorrhoeae; Chlamydia trachomatis; sac-4

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