Confirmatory assays are essential when using molecular testing forNeisseria gonorrhoeaein low-prevalence settings: insights from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3): Table 1

Abstract

ObjectivesTo investigate the occurrence of unconfirmed positive gonorrhoea results when using molecular testing within a large population-based survey.Design, setting and participantsBetween 2010 and 2012, we did a probability sample survey of 15 162 men and women aged 16–74 years in Britain. Urine from participants aged 16–44 years reporting ≥1 lifetime sexual partner was tested for Neisseria gonorrhoeae and Chlamydia trachomatis using the Aptima Combo 2 (AC2) assay, with positive or equivocal results confirmed with molecular assays using different nucleic acid targets.ResultsA total of 4550 participants aged 16–44 years had urine test results (1885 men; 2665 women). For gonorrhoea, 18 samples initially tested positive and eight were equivocal. Only five out of 26 confirmed, giving a positive predictive value (PPV) for the initial testing of 19% (95% CI 4% to 34%). Most (86% (18/21)) participants with unconfirmed positive results for gonorrhoea reported zero or one sexual partner without condoms in the past year and none had chlamydia co-infection, whereas all five with confirmed gonorrhoea reported at least two recent sexual partners without condoms, and four had chlamydia co-infection. The weighted prevalence for gonorrhoea positivity fell from 0.4% (0.3% to 0.7%) after initial screening to <0.1% (0.0% to 0.1%) after confirmatory testing. By comparison, 103 samples tested positive or equivocal for chlamydia and 98 were confirmed (PPV=95% (91% to 99%)).ConclusionsWe highlight the low PPV for gonorrhoea of an unconfirmed reactive test when deploying molecular testing in a low-prevalence population. Failure to undertake confirmatory testing in low-prevalence settings may lead to inappropriate diagnoses, unnecessary treatment and overestimation of population prevalence.

Trends in gonorrhoea positivity by nucleic acid amplification test versus culture among Australian heterosexual men with a low prevalence of gonorrhoea, 2007–2014

“…Furthermore, gonorrhoea positivity identified by culture only remained low (<1%) and stable among heterosexual men attending a large sexual health service in Melbourne over the study period. These findings are consistent with previous studies demonstrating similar effects in women in Australia4 and Britain,5 and indicate that detection for gonorrhoea by NAATs is being used in very low-risk populations when various international guidelines (ie, Australian, US and UK) and the manufacturing guidelines recommend against screening populations with low prevalence of gonorrhoea due to the high likelihood of false positive results 6 7. Our findings support current recommendations that gonorrhoea screening should not be done among asymptomatic heterosexual men unless they report specific behavioural risks such as being a contact of infection.…”

“…If a rise in gonorrhoea notifications was due to an increase in undiagnosed gonorrhoea because of the increased use of dual NAATs, one would not expect the substantial fall in the proportion of gonorrhoea cases detected by NAAT that we observed in our study. The rise in notifications may be due to false positive results from screening a very low-prevalence population of gonorrhoea 6 7. We estimate that about 60% of positives would be false positives using the highest specificity (99.7%) from the Cobas package insert, and a prevalence of gonorrhoea of 0.2%.…”

“…The third National Survey of Sexual Attitudes and Lifestyles (Natsal-3) in 2010–2012 showed that the weighted gonorrhoea prevalence decreased from 0.4% to <0.1% following confirmatory testing of positive screening results among men in the UK 6. Furthermore, a survey from the English National Chlamydia Screening Programme reported that over half (53%) of the practitioners used dual tests on samples for chlamydia testing in the community setting in the UK 5.…”

Risk factors for urethral gonorrhoea infection among heterosexual males in Melbourne, Australia: 2007–17

“…Prior to September 2017, urethral gonorrhoea testing for heterosexual males was only performed at the MSHC for those attending the clinic with urethral symptoms or reported sexual contact with partners with gonorrhoea because gonorrhoea screening is not recommended among heterosexual populations with low prevalence. 9 Oropharyngeal gonorrhoea testing in heterosexual males is not currently recommended as per the Australian sexually transmissible infection (STI) screening guidelines. 10 Urine testing for chlamydia was part of routine STI screening for heterosexual men during the study period.…”

Highlights from this issue

“…The UK's National Survey of Sexual Attitudes and Lifestyles4 is one of very few, and this month Field et al present a detailed analysis of gonorrhoea prevalence and test performance in this large sample 5. The positive predictive value of a nucleic acid amplification test for gonorrhoea is only 19%, by contrast with 95%, due to the rarity of gonorrhoea in an unselected UK population.…”