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NAAT — DFSRH MCQ

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HardNAATDFSRH

A 29-year-old asymptomatic woman attends a specialist sexual health service after condomless vaginal intercourse and receptive oral sex with a new male partner. She has no known contact with gonorrhoea and can reliably attend follow-up. A locally validated NAAT is negative on a self-taken vulvovaginal swab but initially reactive for Neisseria gonorrhoeae on an oropharyngeal swab. The estimated positive predictive value of the initial assay in the clinic's oropharyngeal population is 93%. The assay detects a single gonococcal target, no supplementary test has been performed, and the original specimen remains available. She has not received antibiotics. Which is the most appropriate next sequence?

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Correct answer: A — Test the original specimen using a different gonococcal target, and if confirmed obtain pharyngeal culture before treatment and commence specialist case management

Oropharyngeal infection is the decisive exception to the general PPV threshold. Although supplementary testing may be omitted for genital or rectal specimens when the locally validated PPV is at least 90%, every initially reactive oropharyngeal NAAT requires confirmation because commensal pharyngeal Neisseria species may cross-react. Confirmation should use an alternative molecular target on the original specimen, thereby addressing target-specific non-gonococcal amplification without introducing variability from recollection. If confirmed, pharyngeal culture should be collected before antibiotics wherever possible because culture provides an isolate for phenotypic antimicrobial susceptibility testing; a NAAT does not. Specialist management should then include prompt treatment, partner notification, test of cure and a complete STI screen. A incorrectly extrapolates the PPV rule for genital and rectal specimens to the oropharynx. B repeats the same target and therefore does not adequately address target-specific cross-reactivity. D treats culture as the diagnostic arbiter, although culture is less sensitive than NAAT and a negative result cannot exclude infection. E correctly selects alternative-target testing but prematurely initiates treatment and partner notification. Immediate empirical management could be justified by compelling clinical suspicion or concern that the patient would be lost to follow-up, neither of which applies here.

Reference: Detection of gonorrhoea in England (26 March 2021) — https://www.gov.uk/government/publications/guidance-for-the-detection-of-gonorrhoea-in-england Guidance for the detection of gonorrhoea in England: updated guidance 2021 (March 2021) — https://assets.publishing.service.gov.uk/media/605a11d7d3bf7f2f1608d12b/Guidance_for_the_detection_of_gonorrhoea_in_England_2021.pdf