Confirmatory testing of Neisseria gonorrhoeae in a sexual health clinic: implications for epidemiology and treatment policy.

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European guidelines advise the use of dual nucleic acid amplification tests (NAAT) in order to minimise the inappropriate diagnosis of Neisseria gonorrhoeae (Ng) in urogenital samples from low prevalence areas and in extragenital specimens. In this cross-sectional study, we investigated the effect of confirmatory testing and confirmation policy on the Ng-positivity in a population visiting the sexual health clinic in Rotterdam, the Netherlands.Apart from urogenital testing, extragenital (oropharyngeal/anorectal) testing was performed for men who have sex with men (MSM) and according to sexual exposure for women and heterosexual men. Ng detection using NAAT was performed using BD Viper and for confirmatory testing BD MAX. Sexual transmitted infection consultation data were merged with diagnostic data from August 2015 through May 2016.In women (n=4175), oral testing was performed in 84% and 22% were tested anally. In MSM (n=1828), these percentages were 97% and 96%, respectively. Heterosexual men (n=3089) were tested urogenitally. After confirmatory testing, oropharyngeal positivity rates decreased from 7.3% (95% CI 6.5 to 8.2) to 1.5% (95% CI 1.1 to 1.8) in women and from 13.9% (95% CI 12.3 to 15.5) to 5.4% (95% CI 4.3 to 6.4) in MSM. Anorectal positivity rates decreased from 2.6% (95% CI 1.6 to 3.7) to 1.8% (95% CI 0.9 to 2.6) in women and from 9.3% (95% CI 7.9 to 10.7) to 7.2% (95% CI 6.0 to 8.5) in MSM. Urogenital Ng-positivity rate ranged between 3.0% and 4.4% and after confirmation between 2.3% and 3.9%. When confirming oropharyngeal samples, Ng-positivity was 3.8% in women, 3.0% in heterosexual men and 12.5% in MSM. Additional confirmation of urogenital and anorectal samples led to 3.0% Ng positivity in women, 2.7% in heterosexual men and 11.4% in MSM.Confirmation of urogenital and anorectal samples reduced the Ng-positivity rates, especially for women. However, as there is no gold standard for the confirmation of Ng infection, the dilemma within public health settings is to choose between two evils: missing diagnoses or overtreatment. In view of the large decrease in oropharyngeal positivity, confirmation Ng-positivity in oropharyngeal samples remains essential to avoid unnecessary treatment.

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Authors: Myrte Tielemans, Mireille van Westreenen, Corné Klaassen, Hannelore M Götz