Confirmatory assays are essential when using molecular testing for Neisseria gonorrhoeae in low-prevalence settings: insights from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3)

Nigel Field; Soazig Clifton; Sarah Alexander; Catherine A Ison; Gwenda Hughes; Simon Beddows; Clare Tanton; Kate Soldan; Filomeno Coelho da Silva; Catherine H Mercer; Kaye Wellings; Anne M Johnson; Pam Sonnenberg

doi:10.1136/sextrans-2014-051850

Confirmatory assays are essential when using molecular testing for Neisseria gonorrhoeae in low-prevalence settings: insights from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3)

Sex Transm Infect. 2015 Aug;91(5):338-41. doi: 10.1136/sextrans-2014-051850. Epub 2014 Dec 15.

Authors

Affiliations

¹ Research Department of Infection & Population Health, University College London, Mortimer Market Centre, London, UK.
² Research Department of Infection & Population Health, University College London, Mortimer Market Centre, London, UK NatCen Social Research, London, UK.
³ Sexually Transmitted Bacteria Reference Unit, Public Health England, London, UK.
⁴ Public Health England, National Centre for Infectious Disease Surveillance and Control, London, UK.
⁵ Virus Reference Department, Public Health England, London, UK.
⁶ Department of Social and Environmental Research, London School of Hygiene & Tropical Medicine, London, UK.

Abstract

Objectives: To investigate the occurrence of unconfirmed positive gonorrhoea results when using molecular testing within a large population-based survey.

Design, setting and participants: Between 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.

Results: A 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%)).

Conclusions: We 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.

Keywords: EPIDEMIOLOGY (CLINICAL); NEISSERIA GONORRHOEA; PUBLIC HEALTH; TESTING.

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Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Chlamydia Infections / epidemiology*
Chlamydia trachomatis / isolation & purification*
Female
Gonorrhea / epidemiology*
Health Surveys
Humans
Life Style
Male
Middle Aged
Neisseria gonorrhoeae / isolation & purification*
Nucleic Acid Amplification Techniques
Population Surveillance
Prevalence
Risk Factors
Sexual Behavior
United Kingdom / epidemiology

Abstract

Publication types

MeSH terms

Grants and funding